STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net Income (Loss)	$ 25,936	$ 3,009	$ 74,887	$ 2,106
Net unrealized gains (losses) on available-for-sale securities
Net unrealized holding gains (losses) arising during the period	1,592	(796)	26,039	88,613
Reclassification adjustment for (gains) losses included in net income (loss)		1,775	(79)	43
Total net unrealized gains (losses) on available-for-sale securities	1,592	979	25,960	88,656
Net unrealized gains (losses) on cash flow hedges
Net unrealized gains (losses) on cash flow hedges arising during the period	(1,803)	(3,101)	888	(2,961)
Reclassification adjustment for (gains) losses included in net income (loss)	63	305	683	621
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Total	(1,740)	(2,796)	1,571	(2,340)
Net unrealized other-than-temporary impairments on securities
Change in previously recognized unrealized other-than-temporary impairments	407	1,064	1,076	309
Reclassification adjustment for other-than-temporary impairments included in net income (loss)				121
Net unrealized other-than-temporary impairments on securities	407	1,064	1,076	430
Adjustments
Value of business acquired	(780)	(3,072)	(4,739)	(15,488)
Total other comprehensive income (loss), net of taxes	(521)	(3,825)	23,868	71,258
Comprehensive Income (Loss)	$ 25,415	$ (816)	$ 98,755	$ 73,364