CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 176,186	$ 203,865	$ 219,267
Available-for-sale investments:
Net unrealized gain (loss), net of tax of $981, $515, and ($188) in 2020 2019, and 2018, respectively	6,478	5,219	(1,185)
Reclassification of net realized (gain) loss into current operations	(4,119)	(1,452)	(501)
Net change related to available-for-sale investments	2,359	3,767	(1,686)
Foreign currency translation adjustments:
Foreign currency translation adjustments	1,115	(541)	(4,216)
Net change related to foreign currency translation adjustments	1,115	(541)	(4,216)
Other comprehensive income (loss), net of tax	3,474	3,226	(5,902)
Total comprehensive income	$ 179,660	$ 207,091	$ 213,365