Accumulated Other Comprehensive Income - Schedule of Changes In Each Component of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 691,685	$ 685,228	$ 701,106	$ 657,983
Other comprehensive income (loss), net of tax	6,938	3,569	(8,667)	25,189
Ending balance	695,476	693,750	695,476	693,750
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(5,661)	(6,270)	(5,661)	(6,270)
Ending balance	(5,661)	(6,270)	(5,661)	(6,270)
Securities available-for-sale:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	21,289	33,730	36,894	12,110
Other comprehensive income before reclassifications	6,960	3,565	(8,430)	24,036
Amounts reclassified from other comprehensive income	(22)	4	(237)	(44)
Reclassification of unrealized gains on held-to-maturity securities to available-for-sale		0		1,197
Other comprehensive income (loss), net of tax	6,938	3,569	(8,667)	25,189
Ending balance	28,227	37,299	28,227	37,299
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	15,628	27,460	31,233	5,840
Other comprehensive income before reclassifications	6,960	3,565	(8,430)	24,036
Amounts reclassified from other comprehensive income	(22)	4	(237)	(44)
Reclassification of unrealized gains on held-to-maturity securities to available-for-sale		0		1,197
Other comprehensive income (loss), net of tax	6,938	3,569	(8,667)	25,189
Ending balance	$ 22,566	$ 31,029	$ 22,566	$ 31,029