Accumulated Other Comprehensive Income - Schedule of Changes In Each Component of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 701,106	$ 657,983
Other comprehensive (loss) income, net of tax	(15,605)	21,620
Ending balance	691,685	685,228
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(5,661)	(6,270)
Ending balance	(5,661)	(6,270)
Securities available-for-sale:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	36,894	12,110
Other comprehensive income before reclassifications	(15,390)	20,471
Amounts reclassified from other comprehensive income	(215)	(48)
Reclassification of unrealized gains on held-to-maturity securities to available-for-sale		1,197
Other comprehensive (loss) income, net of tax	(15,605)	21,620
Ending balance	21,289	33,730
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	31,233	5,840
Other comprehensive income before reclassifications	(15,390)	20,471
Amounts reclassified from other comprehensive income	(215)	(48)
Reclassification of unrealized gains on held-to-maturity securities to available-for-sale		1,197
Other comprehensive (loss) income, net of tax	(15,605)	21,620
Ending balance	$ 15,628	$ 27,460