Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 15,087	$ 14,218	$ 36,949	$ 41,168
Other comprehensive income (loss), net of tax:
Unrealized (losses) gains on debt securities available for sale	(2,913)	4,915	22,705	28,302
Accretion of unrealized (loss) gain on debt securities reclassified as held to maturity	(4)	2	1	10
Reclassification adjustment for gains included in net income	0	965	289	1,325
Total other comprehensive (loss) income, net of tax	(2,917)	5,882	22,995	29,637
Derivatives, net of tax:
Unrealized gain (loss) on swap contracts accounted for as cash flow hedges	1,785	(1,279)	(10,314)	(8,735)
Total derivative, net of tax	1,785	(1,279)	(10,314)	(8,735)
Employee benefit plans, net of tax:
Amortization of prior service cost included in net income	(11)	(11)	(32)	(33)
Reclassification adjustment of actuarial net gain included in net income	(846)	(735)	(2,539)	(2,196)
Change in funded status of retirement obligations	(32,733)	1,490	(29,304)	(2,200)
Total employee benefit plans, net of tax	(33,590)	744	(31,875)	(4,429)
Total other comprehensive income (loss)	(34,722)	5,347	(19,194)	16,473
Total comprehensive income (loss), net of tax	$ (19,635)	$ 19,565	$ 17,755	$ 57,641