CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 3,196	$ 8,680	$ (68,010)	$ 41,088
Change in net unrealized gains (losses) related to available-for-sale securities	(2,692)	(26,771)	89,334	(87,336)
Amounts related to cash flow hedges:
Change in net unrealized (losses) gains	(7,648)	7,580	(22,945)	46,385
Reclassification adjustment for amounts included in net income (loss)	(2,702)	(11,162)	(19,624)	(25,776)
Other comprehensive income	(13,042)	(30,353)	46,765	(66,727)
Comprehensive loss	$ (9,846)	$ (21,673)	$ (21,245)	$ (25,639)