Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 15,097	$ 12,031	$ 21,862	$ 26,950
Other comprehensive income, net of tax:
Unrealized gains on debt securities available for sale	6,352	14,092	25,619	23,387
Accretion of unrealized (loss) gain on debt securities reclassified as held to maturity	(2)	(2)	4	8
Reclassification adjustment for gains included in net income	0	260	289	360
Total other comprehensive (loss) income, net of tax	6,350	14,350	25,912	23,755
Derivatives, net of tax:
Unrealized (loss) on swap contracts accounted for as cash flow hedges	(750)	(4,676)	(12,099)	(7,456)
Total derivative, net of tax	(750)	(4,676)	(12,099)	(7,456)
Employee benefit plans, net of tax:
Amortization of prior service cost included in net income	(11)	(11)	(22)	(22)
Reclassification adjustment of actuarial net gain included in net income	(845)	(731)	(1,692)	(1,461)
Change in funded status of retirement obligations	1,714	(4,431)	3,429	(3,690)
Total employee benefit plans, net of tax	858	(5,173)	1,715	(5,173)
Total other comprehensive income	6,458	4,501	15,528	11,126
Total comprehensive income, net of tax	$ 21,555	$ 16,532	$ 37,390	$ 38,076