STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net Income (Loss)	$ (2,137)	$ 24,135	$ 9,828	$ 48,951
Net unrealized gains (losses) on available-for-sale securities
Net unrealized holding gains (losses) arising during the period	(13,617)	18,451	(57,810)	24,447
Reclassification adjustment for (gains) losses included in net income (loss)	(910)	(611)	(12,360)	(79)
Total net unrealized gains (losses) on available-for-sale securities	(14,527)	17,840	(70,170)	24,368
Net unrealized gains (losses) on cash flow hedges
Net unrealized gains (losses) on cash flow hedges arising during the period	(2,908)	2,530	(1,116)	2,691
Reclassification adjustment for (gains) losses included in net income (loss)	2,700	373	1,397	620
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax, Total	(208)	2,903	281	3,311
Net unrealized other-than-temporary impairments on securities
Change in previously recognized unrealized other-than-temporary impairments	(61)	746	(67)	669
Net unrealized other-than-temporary impairments on securities	(61)	746	(67)	669
Adjustments
Value of business acquired	4,288	(3,088)	13,072	(3,959)
Other Comprehensive Income, Adjustments	4,288	(3,088)	13,072	(3,959)
Total other comprehensive income (loss), net of taxes	(10,508)	18,401	(56,884)	24,389
Comprehensive Income (Loss)	$ (12,645)	$ 42,536	$ (47,056)	$ 73,340