Consolidated Statements Of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 59,486	$ 57,203	$ 53,071
Other comprehensive income (loss):
Net change in unrealized gain (loss) on available-for-sale debt securities, net of tax	26,060	21,076	(7,993)
Net change in unrealized loss on cash flow hedging derivatives, net of tax	1,422	(1,611)	1,489
Net unrecognized (loss) gain on postretirement plans, net of tax	(474)	(1,313)	1,831
Other comprehensive income (loss)	27,008	18,152	(4,673)
Comprehensive income	$ 86,494	$ 75,355	$ 48,398