Accumulated amortization: Finite-Lived Intangible Assets, Accumulated Amortization Schedule of Intangible Assets Schedule Of Intangible Assets [Table Text Block] Tabular disclosure of assets, excluding financial assets and goodwill, lacking physical substance, by either major class or business segment. Accrued liabilities for executive and employee incentive compensation Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities Investments Investment, Policy [Policy Text Block] Debt Instrument, Redemption, Period Four Debt Instrument, Redemption, Period Four [Member] Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Cash Flows Schedule of Expected Benefit Payments [Table Text Block] Prime Rate or Canadian Prime Rate Prime Rate Or Canadian Prime Rate [Member] Prime Rate Or Canadian Prime Rate Award Timing Predetermined Award Timing Predetermined [Flag] Thrift Plan and MII Thrift Plan Thrift Plan And Mii Thrift Plan [Member] Thrift plan and MII thrift plan. 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Recently Adopted Accounting Standards and New Accounting and Disclosure Standard New Accounting Pronouncements, Policy [Policy Text Block] U.S. research and development tax credit Effective Income Tax Rate Reconciliation, Tax Credit, Research, Amount Goodwill [Line Items] Goodwill [Line Items] Adjustment to Compensation: Adjustment to Compensation [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Revenue Recognition Revenue from Contract with Customer [Text Block] Convertible Senior Notes Due 2030 2030 Notes [Member] 2030 Notes Risks and Uncertainties Risks And Uncertainties [Text Block] Risks and uncertainties text block. Total current Current Income Tax Expense (Benefit) Adjustment to Compensation, Amount Adjustment to Compensation Amount Concentration risk percentage Concentration Risk, Percentage Pension Benefits Pension Plan [Member] Revenue, remaining performance obligation, percentage Revenue, Remaining Performance Obligation, Percentage Stock-based compensation expense Share-Based Payment Arrangement, Noncash Expense Stock Option Share-Based Payment Arrangement, Option [Member] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Effective Income Tax Rate Reconciliation, Percent [Abstract] Effective Income Tax Rate Reconciliation, Percent [Abstract] Investments Long Term Investments Excluding Investments In Unconsolidated Affiliates Long term investments excluding investments in unconsolidated affiliates. Rates to which the cost trend rate is assumed to decline (ultimate trend rate) Defined Benefit Plan, Ultimate Health Care Cost Trend Rate Stockholders' Equity – BWX Technologies, Inc. Equity, Attributable to Parent Unrealized (losses) gains arising during the period, tax provision Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, Tax Debt Securities, Available-for-Sale [Table] Debt Securities, Available-for-Sale [Table] Insider Trading Policies and Procedures [Line Items] Property, Plant and Equipment Property, Plant and Equipment [Table Text Block] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Other comprehensive (income) loss, pension benefits and other benefits Defined Benefit Plan Amounts Recognized In Net Periodic Benefit Cost And Other Comprehensive (Income) Loss Defined benefit plan amounts recognized in net periodic benefit cost and other comprehensive loss income. Percentage of investment return on domestic plan assets Defined Benefit Plan Percentage Of Investment Return On Plan Assets Defined benefit plan, percentage of investment return on plan assets. 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Stock-Based Compensation Share-Based Payment Arrangement [Policy Text Block] Trading Symbol Trading Symbol 2029 Lessee, Operating Lease, Liability, to be Paid, Year Four Stock-based compensation charges (in shares) Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Entity Address, City or Town Entity Address, City or Town EFFECTS OF EXCHANGE RATE CHANGES ON CASH Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Foreign currency exchange rate changes Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss) Total deferred tax assets Deferred Tax Assets, Net of Valuation Allowance Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Restricted Stock Units Restricted Stock Units (RSUs) [Member] Letter of credit fee Letter Of Credit Fee, Commitment Fee Percentage Letter Of Credit Fee, Commitment Fee Percentage Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Acquisitions Defined Benefit Plan, Plan Assets, Business Combination Purchase of business Business Combination, Consideration Transferred Decreases due to settlements with tax authorities Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Schedule of Intangible Assets Acquired Business Combination, Intangible Asset, Acquired, Finite-Lived [Table Text Block] Entity Emerging Growth Company Entity Emerging Growth Company Maturity of long-term debt, year three Long-Term Debt, Maturity, Year Three Outstanding at beginning of period (shares) Outstanding at end of period (shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Balance at beginning of period Balance at end of period Debt issuance costs Less: Deferred debt issuance costs Debt Issuance Costs, Net Restricted cash and cash equivalents Restricted Cash and Cash Equivalent 2026 Defined Benefit Plan, Expected Future Benefit Payment, Year One Discount rate to determine interest cost Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate To Determine Interest Cost Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate To Determine Interest Cost Unamortized intangible assets: Indefinite-Lived Intangible Assets (Excluding Goodwill) Schedule Of Amortized And Unamortized Intangible Assets [Line Items] Schedule Of Amortized And Unamortized Intangible Assets [Line Items] Schedule of amortized and unamortized intangible assets [Line Items] Summary of Investments Marketable Securities [Table Text Block] Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Prepaid pension Assets for Plan Benefits, Defined Benefit Plan Bonds issued and outstanding Bonds Issued And Outstanding Bonds issued and outstanding. Exercises of stock options Stock Issued During Period, Value, Stock Options Exercised Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Service term requirement Defined Benefit Plan, Eligibility Requirement, Continuous Service Term Defined Benefit Plan, Eligibility Requirement, Continuous Service Term Schedule of Property, Plant and Equipment, Net by Geographical Area Schedule of Disclosure on Geographic Areas, Long-Lived Assets in Individual Foreign Countries by Country [Table Text Block] Estimated Amortization Expense Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Change in benefit obligation: Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Number of Shares Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Provision for Income Taxes Provision for Income Taxes Provision for income taxes Provision for Income Taxes Income Tax Expense (Benefit) Debt instrument, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Contingencies And Commitments [Line Items] Contingencies And Commitments [Line Items] Contingencies and commitments line items Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Derivative financial instruments Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Property plant and equipment gross Property, Plant and Equipment, Gross Property, Plant and Equipment Property, Plant and Equipment [Member] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Operating Income Increase (decrease) in operating income Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Modification of Contract SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] Income taxes Increase (Decrease) in Income Taxes Acquisition of businesses Payments to Acquire Businesses, Net of Cash Acquired U.S. – federal Income Tax Paid, Federal, after Refund Received All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Share Repurchase Program Share Repurchase Program [Member] Share Repurchase Program [Member] Redemption price percentage Debt Instrument, Redemption Price, Percentage U.S. federal tax credits and loss carryforward Deferred Tax Assets, Operating Loss Carryforwards, Domestic Loss Contingencies Commitments and Contingencies, Policy [Policy Text Block] Other Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Nonvested cash-settled performance units (in shares) Nonvested at beginning of period (in shares) Nonvested at end of period (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Accumulated benefit obligation Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Accumulated Benefit Obligation Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Warranty Expense Standard Product Warranty, Policy [Policy Text Block] NET CASH PROVIDED BY OPERATING ACTIVITIES Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Amounts recognized in the balance sheet consist of: Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position [Abstract] Increase (decrease) in goodwill Goodwill, Period Increase (Decrease) Estimated Fair Value Available-for-sale securities Debt Securities, Available-for-Sale, Excluding Accrued Interest Effective Income Tax Rate Reconciliation [Table] Effective Income Tax Rate Reconciliation [Table] Equity Method Investments and Joint Ventures [Abstract] Equity Method Investments and Joint Ventures [Abstract] Useful life (in years) Property, Plant and Equipment, Useful Life Preferred stock, par value (usd per share) Preferred Stock, Par or Stated Value Per Share Revenues from External Customers and Long-Lived Assets [Line Items] Revenues from External Customers and Long-Lived Assets [Line Items] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Depreciation Depreciation Debt Instrument, Redemption, Period Three Debt Instrument, Redemption, Period Three [Member] Diluted: Net Income (Loss) Available to Common Stockholders, Diluted [Abstract] Equity Components [Axis] Equity Components [Axis] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Convertible Debt Convertible Debt [Member] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Investment, reclassification adjustment, tax provision Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] Number of reportable segments Number of Reportable Segments Accumulated benefit obligation Defined Benefit Plan Plans With Assets In Excess Of Accumulated Benefit Obligation Aggregate Accumulated Benefit Obligation Defined benefit plan, plans with assets in excess of accumulated benefit obligation, aggregate accumulated benefit obligation. Deferred tax assets: Components of Deferred Tax Assets [Abstract] Entity Address, State or Province Entity Address, State or Province Accumulated Postretirement Benefit Obligation Accumulated postretirement benefit obligation Liability, Other Postretirement Defined Benefit Plan, Noncurrent Investments in Unconsolidated Affiliates Equity Method Investments Issuances, Policy [Policy Text Block] 2029 Defined Benefit Plan, Expected Future Benefit Payment, Year Four Total Current Liabilities Liabilities, Current Individual: Individual [Axis] Employer contributions Defined Contribution Plan, Cost Income Tax Jurisdiction [Domain] Income Tax Jurisdiction [Domain] Asset Retirement Obligations Schedule of Asset Retirement Obligations [Table Text Block] Dividends paid to common shareholders Payments of Ordinary Dividends, Common Stock Document Annual Report Document Annual Report Amortization Amortization Settlements Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement Financial assurance to pay expected cost of decommissioning Financial Assurance To Pay Expected Cost Of Decommissioning Financial assurance to pay expected cost of decommissioning. Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Repayments of long-term debt Repayments of Long-Term Debt Entity Interactive Data Current Entity Interactive Data Current Mutual funds Mutual Fund [Member] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Funded status Defined Benefit Plan, Funded (Unfunded) Status of Plan Exercisable at end of period, aggregate intrinsic value Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value Other comprehensive (income) loss, net periodic benefit cost Defined Benefit Plan Amounts Recognized In Net Periodic Pension Cost And Other Comprehensive (Income) Loss Defined benefit plan amounts recognized in net periodic pension cost and other comprehensive income. Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Federal capital losses Deferred Tax Assets, Operating Loss Carryforwards Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset [Axis] Advanced Reactor Design and Engineering Commercial Operations [Member] Commercial operations. Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Beginning Balance Ending Balance SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Investees Investee [Member] 2027 Defined Benefit Plan, Expected Future Benefit Payment, Year Two Other Assets Other Assets, Noncurrent Debt Instrument, Convertible Terms Of Conversion [Axis] Debt Instrument, Convertible Terms Of Conversion [Axis] Debt Instrument, Convertible Terms Of Conversion Customer [Domain] Customer [Domain] Entity Central Index Key Entity Central Index Key Thrift Plan Thrift Plan [Member] Thrift plan. PEO Name PEO Name Conversion price (in usd per share) Debt Instrument, Convertible, Conversion Price Revenues Revenues Balance at beginning of period Balance at end of period Asset Retirement Obligation Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Defined Benefit Plan [Table] Defined Benefit Plan [Table] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Revenues Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price Contract with customer, liability Contract with Customer, Liability, Current Product warranty accrual, current Product Warranty Accrual, Current Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Benefits paid Defined Benefit Plan, Benefit Obligation, Benefits Paid U.S. federal statutory tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Investments in joint ventures and affiliated companies Deferred Tax Assets, Equity Method Investments Long-Term Debt Long-Term Debt Long-Term Debt, Excluding Current Maturities Statement of Financial Position Location, Balance [Axis] Statement of Financial Position Location, Balance [Axis] 2028 Finite-Lived Intangible Asset, Expected Amortization, Year Three Amortized intangible assets: Finite-Lived Intangible Assets, Gross Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Entity Address, Address Line One Entity Address, Address Line One Research and development costs Research and Development Expense Accumulated Other Comprehensive Income (Loss) Accumulated other comprehensive income (loss) AOCI Attributable to Parent [Member] Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract] Recognized (gain) loss on foreign currency derivative instruments not designated as hedging instruments Gain (Loss) on Foreign Currency Derivative Instruments Not Designated as Hedging Instruments Amortization of prior service cost Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Fair Value as of Grant Date Award Grant Date Fair Value Amortized Cost Equity Securities, FV-NI, Cost Other comprehensive income (loss), Gain (loss), reclassification, tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax Pension Plans Postretirement And Other Employee Benefits [Table] Pension Plans Postretirement And Other Employee Benefits [Table] Pension Plans Postretirement And Other Employee Benefits [Table] Net operating loss carryforwards Operating Loss Carryforwards Changes in unrecognized tax benefits Effective Income Tax Rate Reconciliation, Tax Contingency, Amount Environmental Loss Contingency Statement Of Financial Position Extensible Enumeration Not Disclosed Flag Environmental Loss Contingency Statement Of Financial Position Extensible Enumeration Not Disclosed Flag Environmental Loss Contingency Statement Of Financial Position Extensible Enumeration Not Disclosed Flag Stock options, restricted stock units and performance shares (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Purchases of securities Payments to Acquire Investments Total Costs and Expenses Costs and Expenses Cancelled/forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Total unrecognized estimated compensation expense, nonvested awards Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Provision for deferred taxes Deferred Income Taxes and Tax Credits Fair value of senior notes Long-Term Debt, Fair Value Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] 2027 Lessee, Operating Lease, Liability, to be Paid, Year Two Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Outstanding at end of period, weighted-average remaining contractual term (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Price per share of common stock, capped call transaction (in usd per share) Debt Instrument, Capped Call Transaction, Price Cap Per Share Of Common Stock Debt Instrument, Capped Call Transaction, Price Cap Per Share Of Common Stock Schedule of Transactions with Unconsolidated Affiliates Investments in and Advances to Affiliates [Table Text Block] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount 2028 Defined Benefit Plan, Expected Future Benefit Payment, Year Three Other: Other Geographic Location [Member] Other [Member] Non-PEO NEO Non-PEO NEO [Member] Outstanding at end of period, aggregate intrinsic value Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value Letters of credit outstanding, amount Letters of Credit Outstanding, Amount Current asset retirement obligation Asset Retirement Obligation, Current Other – net Other Income (Expense), Net Other income expense net. All other Other Intangible Assets [Member] Gross Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Land Land [Member] Award Type [Domain] Award Type [Domain] Unrecognized prior service cost on benefit obligations Amortization of prior service cost on benefit obligations Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] 2026 Lessee, Operating Lease, Liability, to be Paid, Year One Noncontrolling interest Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Effect of cross-border tax laws Effective Income Tax Rate Reconciliation, Cross-Border Tax Effect, Percent Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Canada: Canada CANADA Accounts receivable Increase (Decrease) in Accounts and Other Receivables Compensation Amount Outstanding Recovery Compensation Amount Deferred Finance Costs [Roll Forward] Deferred Finance Costs [Roll Forward] Deferred Finance Costs [Roll Forward] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Minimum percentage of fair market value closing price Minimum Percentage of Fair Market Value Closing Price Minimum percentage of fair market value closing price. Summary of Combined Income Statement Information Equity Method Investment Combined Income Statement Information [Table Text Block] Tabular disclosure of equity method investments including combined summarized income statement information. Foreign Exchange Contracts Foreign Exchange Contract [Member] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Advanced billings revenue recognized Contract with Customer, Liability, Revenue Recognized Retirement Plan Type [Domain] Retirement Plan Type [Domain] Charges To Costs and Expenses SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Canada - capital loss realization Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent Investments: Debt Securities, Unrealized Gain (Loss) [Abstract] Pension liability Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions Total Costs and Expenses Costs and Expenses, Adjusted Costs and Expenses, Adjusted Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block] Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Changes in Carrying Amount of Intangible Assets Schedule Of Changes In Carrying Amount Of Other Intangible Assets [Table Text Block] Schedule of changes in carrying amount of other intangible assets. Plans with plan assets in excess of accumulated benefit obligation: Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract] Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Investments, net of return of capital, in equity method investees Payments To (Proceeds) From Equity Method Investments, Net Of Return Of Capital Payments To (Proceeds) From Equity Method Investments, Net Of Return Of Capital Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] Maturity of long-term debt, year one Long-Term Debt, Maturity, Year One Financial Instruments [Domain] Financial Instruments [Domain] Available-for-sale investments OCI, Debt Securities, Available-for-Sale, Gain (Loss), after Adjustment and Tax Environmental Matters Environmental Matters [Member] Environmental matters. Total deferred tax liabilities Deferred Tax Liabilities, Gross Maturity of long-term debt, year five Long-Term Debt, Maturity, Year Five Performance Shares Performance Shares [Member] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Less: Amounts due within one year Long-Term Debt, Gross, Current Long-Term Debt, Gross, Current Reclassification adjustment for gains included in net income, net of tax provision of $339, $245 and $91, respectively Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Inventories Inventories Inventory, Net Developed Technology Rights Developed Technology Rights [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Lease liabilities Deferred Tax Assets, Lease Liabilities Deferred Tax Assets, Lease Liabilities Minimum Minimum [Member] Reconciliation of Net Income to Equity in Income Equity Method Investment Reconciliation Of Net Income To Equity In Income [Table Text Block] Tabular disclosure of equity method investments, including the difference between recorded amount of an investment and the value of the underlying equity in the net assets. Year that the rate reaches ultimate trend rate Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate Purchase price adjustment Goodwill, Measurement Period Adjustment Company Selected Measure Name Company Selected Measure Name Environmental reserves Accrual for Environmental Loss Contingencies Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Accounts payable Accounts Payable, Current Cash payments for leases Operating Lease, Payments Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Net Income Attributable to BWX Technologies, Inc. Net Income (Loss) Available to Common Stockholders, Diluted Other than U.S. Current Foreign Tax Expense (Benefit) Goodwill [Roll Forward] Goodwill [Roll Forward] Accrued liabilities for self-insurance (including postretirement health care benefits) Deferred Tax Liabilities, Accrued Liabilities For Self Insurance Deferred Tax Liabilities, Accrued Liabilities For Self Insurance Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Diluted (in shares) Adjusted weighted average common shares (in shares) Weighted Average Number of Shares Outstanding, Diluted Reportable Segments Segment Reporting, Policy [Policy Text Block] Recognition of benefit plan costs, net of tax benefit of $(629), $(344) and $(609), respectively Other Comprehensive Income Defined Benefit Plans Net Gain Loss Recognized In Net Periodic Benefit Cost Net Of Tax Other comprehensive income defined benefit plans net gain loss recognized in net periodic benefit cost net of tax. 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(USD per share) Diluted earnings per common share (USD per share) Earnings Per Share, Diluted Kinectrics Holdings, Inc. Kinectrics Holdings, Inc. [Member] Kinectrics Holdings, Inc. Aerojet Ordnance Tennessee, Inc. Aerojet Ordnance Tennessee, Inc. [Member] Aerojet Ordnance Tennessee, Inc. 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