CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 82,873	$ 108,325	$ 140,820
Amounts related to available-for-sale securities:
Change in net unrealized gains	(48,894)	(98,202)	27,283
Amounts related to cash flow hedges:
Change in net unrealized losses	(1,370)	(21,675)	(41,059)
Reclassification adjustment for amounts included in net income	19,955	28,550	22,055
Other comprehensive income (loss)	(30,309)	(91,327)	8,279
Comprehensive income	$ 52,564	$ 16,998	$ 149,099