Condensed Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 62,259	$ 46,439
Other comprehensive income:
Foreign currency translation adjustments, before tax	(7,627)	1,152
Income tax benefit (expense)	6	(2)
Foreign currency translation adjustments, net of tax	(7,621)	1,150
Changes in employee benefit related items:
Amortization of prior service cost	3	5
Recognized actuarial gain	169	286
Changes in employee benefit related items	172	291
Income tax (expense) benefit	(28)	2
Employee benefit related items, net of tax	144	293
Other	0	0
Other comprehensive (loss) income	(7,477)	1,443
Comprehensive income	$ 54,782	$ 47,882