Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 14,919	$ 11,784
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on debt securities available for sale	9,295	(9,985)
Accretion of unrealized gain on debt securities reclassified as held to maturity	10	19
Reclassification adjustment for gains included in net income	100	88
Total other comprehensive (loss) income, net of tax	9,405	(9,878)
Derivatives, net of tax:
Unrealized (loss) gain on swap contracts	(2,780)
Unrealized (loss) gain on swap contracts		342
Total derivatives, net of tax		342
Employee benefit plans, net of tax:
Amortization of prior service cost included in net income	(25)	(43)
Reclassification adjustment of actuarial net gain (loss) included in net income	130	(102)
Change in funded status of retirement obligations	(105)	(268)
Total employee benefit plans, net of tax	0	(413)
Total other comprehensive income (loss)	6,625	(9,949)
Total comprehensive income, net of tax	$ 21,544	$ 1,835