Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Basic:
Net Income Attributable to BWX Technologies, Inc.	$ 75,499	$ 48,978
Weighted-average common shares (in shares)	95,412,351	95,255,109
Basic earnings per common share (in usd per share)	$ 0.79	$ 0.51
Diluted:
Net Income Attributable to BWX Technologies, Inc.	$ 75,499	$ 48,978
Weighted-average common shares (in shares)	95,412,351	95,255,109
Effect of dilutive securities:
Stock options, restricted stock units and performance shares (in shares)	344,021	566,245
Adjusted weighted-average common shares (in shares)	95,756,372	95,821,354
Diluted earnings per common share (in usd per share)	$ 0.79	$ 0.51
Number of shares that would be antidilutive (in shares)	99,102	181,358

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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