Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (14,742)	$ 9,272	$ (2,958)	$ 19,567
Other comprehensive (loss) income, net of tax:
Unrealized (losses) gains on securities available-for-sale	(2,860)	1,739	(12,828)	2,134
Accretion of unrealized gain on securities reclassified as held-to-maturity	(3)	0	(2)	0
Reclassification adjustment for gains included in net income	0	0	87	0
Total other comprehensive (loss) income, net of tax	(2,863)	1,739	(12,743)	2,134
Derivatives, net of tax
Unrealized gain (loss) on swap contracts	164	(37)	506	(31)
Total derivatives, net of tax	164	(37)	506	(31)
Employee benefit plans, net of tax:
Amortization of prior service cost included in net income	0	0	118	0
Reclassification adjustment of actuarial net loss included in net income	0	(2)	527	(5)
Change in funded status of retirement obligations	2,323	72	1,266	(74)
Total employee benefit plans, net of tax	2,323	70	1,911	(79)
Total other comprehensive (loss) income	(376)	1,772	(10,326)	2,024
Total comprehensive (loss) income, net of tax	$ (15,118)	$ 11,044	$ (13,284)	$ 21,591