CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 103,878	$ 76,371	$ 339,964	$ 241,931
Other comprehensive income (loss):
Unrealized (losses) gains on investments	(1,811)	734	(5,896)	(666)
Unrealized gains on cash flow hedges	6,556	4,814	36,860	7,564
Total unrealized gains	4,745	5,548	30,964	6,898
Income tax expense	(1,219)	(2,113)	(7,562)	(2,644)
Other comprehensive income, net of tax expense	3,526	3,435	23,402	4,254
Total comprehensive income	$ 107,404	$ 79,806	$ 363,366	$ 246,185