STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net Income (Loss)	$ 20,449	$ 25,936	$ 30,277	$ 74,887
Net unrealized gains (losses) on available-for-sale securities
Net unrealized holding gains (losses) arising during the period	(8,868)	1,592	(66,678)	26,039
Reclassification adjustment for (gains) losses included in net income (loss)	(1,212)		(13,572)	(79)
Total net unrealized gains (losses) on available-for-sale securities	(10,080)	1,592	(80,250)	25,960
Net unrealized gains (losses) on cash flow hedges
Net unrealized gains (losses) on cash flow hedges arising during the period	66	(1,803)	(1,050)	888
Reclassification adjustment for (gains) losses included in net income (loss)	165	63	1,562	683
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Total	231	(1,740)	512	1,571
Net unrealized other-than-temporary impairments on securities
Change in previously recognized unrealized other-than-temporary impairments	591	407	524	1,076
Net unrealized other-than-temporary impairments on securities	591	407	524	1,076
Adjustments
Value of business acquired	6,319	(780)	19,391	(4,739)
Total other comprehensive income (loss), net of taxes	(2,939)	(521)	(59,823)	23,868
Comprehensive Income (Loss)	$ 17,510	$ 25,415	$ (29,546)	$ 98,755