STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net Income (Loss)	$ 24,135	$ 5,701	$ 48,951	$ (903)
Net unrealized gains (losses) on available-for-sale securities
Net unrealized holding gains (losses) arising during the period	18,451	40,686	24,447	89,409
Reclassification adjustment for (gains) losses included in net income (loss)	(611)	68	(79)	(1,732)
Total net unrealized gains (losses) on available-for-sale securities	17,840	40,754	24,368	87,677
Net unrealized gains (losses) on cash flow hedges
Net unrealized gains (losses) on cash flow hedges arising during the period	2,530	1,290	2,691	140
Reclassification adjustment for (gains) losses included in net income (loss)	373	513	620	316
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Total	2,903	1,803	3,311	456
Net unrealized other-than-temporary impairments on securities
Change in previously recognized unrealized other-than-temporary impairments	746	100	669	(755)
Reclassification adjustment for other-than-temporary impairments included in net income (loss)				121
Net unrealized other-than-temporary impairments on securities	746	100	669	(634)
Adjustments
Value of business acquired	(3,088)	(7,318)	(3,959)	(12,416)
Other Comprehensive Income, Adjustments	(3,088)	(7,318)	(3,959)	(12,416)
Total other comprehensive income (loss), net of taxes	18,401	35,339	24,389	75,083
Comprehensive Income (Loss)	$ 42,536	$ 41,040	$ 73,340	$ 74,180