CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 288,934	$ 250,327	$ 274,284
Other comprehensive income (loss):
Unrealized losses on investments	(716)	(1,792)	(2,205)
Unrealized gains (losses) on cash flow hedges	19,195	13,764	(5,224)
Total unrealized gains (losses)	18,479	11,972	(7,429)
Income tax (expense) benefit	(7,060)	(4,584)	2,763
Other comprehensive income (losses), net of tax (expense) benefit	11,419	7,388	(4,666)
Total comprehensive income	$ 300,353	$ 257,715	$ 269,618