Condensed Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 81,087	$ 62,259
Other comprehensive (loss) income:
Foreign currency translation adjustments, before tax	(2,732)	(7,627)
Income tax (expense) benefit	(30)	6
Foreign currency translation adjustments, net of tax	(2,762)	(7,621)
Changes in employee benefit related items:
Amortization of prior service cost	(2)	3
Recognized actuarial (loss) gain	(274)	169
Changes in employee benefit related items	(276)	172
Income tax benefit (expense)	2	(28)
Employee benefit related items, net of tax	(274)	144
Other comprehensive (loss)	(3,036)	(7,477)
Comprehensive income	$ 78,051	$ 54,782