Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net Income	$ 73,195	$ 74,998	$ 213,211	$ 183,108
Other Comprehensive Income (Loss):
Currency translation adjustments	8,704	(2,535)	(2,380)	2,703
Derivative financial instruments:
Unrealized gains (losses) arising during the period, net of tax (provision) benefit of $(12), $79, $20 and $469, respectively	32	(248)	(59)	(1,323)
Reclassification adjustment for (gains) losses included in net income, net of tax provision (benefit) of $79, $26, $(27) and $5, respectively	(232)	(72)	99	(10)
Amortization of benefit plan costs, net of tax benefit of $(141), $(130), $(475) and $(421), respectively	688	519	1,907	1,523
Unrealized losses on investments arising during the period, net of tax benefit (provision) of $1, $0, $(1) and $(10), respectively	(81)	(54)	(527)	(3)
Other Comprehensive Income (Loss)	9,111	(2,390)	(960)	2,890
Total Comprehensive Income	82,306	72,608	212,251	185,998
Comprehensive Income Attributable to Noncontrolling Interest	(29)	(188)	(283)	(442)
Comprehensive Income Attributable to BWX Technologies, Inc.	$ 82,277	$ 72,420	$ 211,968	$ 185,556