Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 14,218	$ 10,827	$ 41,168	$ 7,869
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on debt securities available for sale	4,915	(5,358)	28,302	(18,186)
Accretion of unrealized gain (loss) on debt securities reclassified as held to maturity	2	(11)	10	(13)
Reclassification adjustment for gains included in net income	965	3	1,325	90
Total other comprehensive (loss) income, net of tax	5,882	(5,366)	29,637	(18,109)
Derivatives, net of tax:
Unrealized (loss) gain on swap contracts accounted for as cash flow hedges	(1,279)		(8,735)
Unrealized (loss) gain on swap contracts accounted for as cash flow hedges		1,240		1,746
Total derivatives, net of tax		1,240		1,746
Employee benefit plans, net of tax:
Amortization of prior service cost included in net income	(11)	0	(33)	98
Reclassification adjustment of actuarial net (loss) gain included in net income	(735)	0	(2,196)	520
Change in funded status of retirement obligations	1,490	(1,908)	(2,200)	(615)
Total employee benefit plans, net of tax	744	(1,908)	(4,429)	3
Total other comprehensive income (loss)	5,347	(6,034)	16,473	(16,360)
Total comprehensive income (loss), net of tax	$ 19,565	$ 4,793	$ 57,641	$ (8,491)