Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 385,843	$ 279,380	$ 238,563
Other comprehensive (loss) income:
Foreign currency translation adjustments, before reclassification and tax	(2,894)	8,579	1,900
Less: reclassification adjustment for gains (losses) included in net income upon liquidation	1,613	(77)	0
Foreign currency translation adjustments, before tax	(4,507)	8,656	1,900
Income tax benefit (expense)	147	(310)	(161)
Foreign currency translation adjustments, net of tax	(4,360)	8,346	1,739
Changes in employee benefit related items:
Amortization of prior service cost	7	8	6
Recognized actuarial gain (loss)	5,566	(1,557)	(3,011)
Changes in employee benefit related items	5,573	(1,549)	(3,005)
Income tax (expense) benefit	(20)	(67)	99
Employee benefit related items, net of tax	5,553	(1,616)	(2,906)
Other comprehensive income (loss)	1,193	6,730	(1,167)
Comprehensive income	$ 387,036	$ 286,110	$ 237,396