Accumulated Other Comprehensive Loss - Schedule of Changes In Each Component of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Nine months ended September 30,
Beginning Balance	$ 693,750	$ 636,908	$ 657,983	$ 600,764
Other comprehensive income	(539)	6,307	24,650	25,877
Ending balance	691,359	649,603	691,359	649,603
Defined Benefit Pension Plans
Nine months ended September 30,
Beginning Balance	(6,270)	(5,871)	(6,270)	(5,871)
Ending balance	(6,270)	(5,871)	(6,270)	(5,871)
Securities available-for-sale:
Nine months ended September 30,
Beginning Balance	37,299	10,959	12,110	(8,611)
Other comprehensive income before reclassifications	(539)	6,277	23,497	25,931
Amounts reclassified from other comprehensive income	0	30	(44)	(54)
Reclassification of unrealized gains on held-to-maturity securities to available-for-sale	0		1,197
Other comprehensive income	(539)	6,307	24,650	25,877
Ending balance	36,760	17,266	36,760	17,266
Total
Nine months ended September 30,
Beginning Balance	31,029	5,088	5,840	(14,482)
Other comprehensive income before reclassifications	(539)	6,277	23,497	25,931
Amounts reclassified from other comprehensive income	0	30	(44)	(54)
Reclassification of unrealized gains on held-to-maturity securities to available-for-sale	0		1,197
Other comprehensive income	(539)	6,307	24,650	25,877
Ending balance	$ 30,490	$ 11,395	$ 30,490	$ 11,395