CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 219,267	$ 176,712	$ 143,694
Cash flow hedges:
Net unrealized gain (loss), net of tax of $0, ($5), and ($22) in 2018, 2017, and 2016, respectively	0	4	(567)
Reclassification of net realized (gain) loss into current operations	0	(41)	398
Net change related to cash flow hedges	0	(37)	(169)
Available-for-sale investments:
Net unrealized gain (loss), net of tax of $188, $2, and $248 in 2018, 2017, and 2016, respectively	(1,185)	703	1,672
Reclassification of net realized (gain) loss into current operations	(501)	(829)	(191)
Net change related to available-for-sale investments	(1,686)	(126)	1,481
Foreign currency translation adjustments:
Foreign currency translation adjustments, net of tax of $0, $0 and ($228) in 2018, 2017, and 2016, respectively	(4,216)	21,992	(5,616)
Net change related to foreign currency translation adjustments	(4,216)	21,992	(5,616)
Other comprehensive income gain (loss), net of tax	(5,902)	21,829	(4,304)
Total comprehensive income	$ 213,365	$ 198,541	$ 139,390