CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 250,327	$ 274,284	$ 193,785
Other comprehensive income (loss):
Unrealized (losses) gains on investments	(1,792)	(2,205)	6,066
Unrealized gains (losses) on cash flow hedges	13,764	(5,224)	(19,772)
Total unrealized gains (losses)	11,972	(7,429)	(13,706)
Income tax (expense) benefit	(4,584)	2,763	5,337
Other comprehensive income (losses), net of tax (expense) benefit	7,388	(4,666)	(8,369)
Total comprehensive income (loss)	$ 257,715	$ 269,618	$ 185,416