CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net (loss) income	$ (7,746)	$ 19,420
Amounts related to available-for-sale securities:
Change in net unrealized gains (losses)	43,476	(44,053)
Amounts related to derivative instruments held as cash flow hedges:
Change in net unrealized (losses) gains	(8,551)	30,933
Reclassification adjustment for amounts included in net (loss) income	(10,571)	(4,644)
Other comprehensive income	24,354	(17,764)
Comprehensive income	$ 16,608	$ 1,656

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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