Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 10,827	$ 1,514	$ 7,869	$ 21,080
Other comprehensive (loss) income, net of tax:
Unrealized (losses) gains on securities available-for-sale	(5,358)	3,266	(18,186)	5,399
Accretion of unrealized gain on securities reclassified as held-to-maturity	(11)	(258)	(12)	(258)
Reclassification adjustment for gains included in net income	3	0	90	0
Total other comprehensive (loss) income, net of tax	(5,366)	3,008	(18,108)	5,141
Derivatives, net of tax
Unrealized gain on swap contracts	1,240	93	1,746	62
Total derivatives, net of tax	1,240	93	1,746	62
Employee benefit plans, net of tax:
Amortization of prior service cost included in net income	0	0	98	(1)
Reclassification adjustment of actuarial net loss included in net income	0	25	519	1,379
Change in funded status of retirement obligations	(1,908)	14,832	(615)	13,401
Total employee benefit plans, net of tax	(1,908)	14,857	2	14,779
Total other comprehensive (loss) income	(6,034)	17,958	(16,360)	19,982
Total comprehensive income (loss), net of tax	$ 4,793	$ 19,472	$ (8,491)	$ 41,062