Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 12,031	$ (14,742)	$ 26,950	$ (2,958)
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on debt securities available for sale	14,092	(2,860)	23,387	(12,829)
Accretion of unrealized (loss) gain on debt securities reclassified as held to maturity	(2)	(3)	8	(2)
Reclassification adjustment for gains included in net income	260	0	360	88
Total other comprehensive (loss) income, net of tax	14,350	(2,863)	23,755	(12,743)
Derivatives, net of tax:
Unrealized (loss) gain on swap contracts accounted for as cash flow hedges	(4,676)		(7,456)
Unrealized (loss) gain on swap contracts accounted for as cash flow hedges		164		506
Total derivatives, net of tax		164		506
Employee benefit plans, net of tax:
Amortization of prior service cost included in net income	(11)	0	(22)	118
Reclassification adjustment of actuarial net (loss) gain included in net income	(731)	0	(1,461)	527
Change in funded status of retirement obligations	(4,431)	2,323	(3,690)	1,266
Total employee benefit plans, net of tax	(5,173)	2,323	(5,173)	1,911
Total other comprehensive income (loss)	4,501	(376)	11,126	(10,326)
Total comprehensive income (loss), net of tax	$ 16,532	$ (15,118)	$ 38,076	$ (13,284)