Accumulated Other Comprehensive Loss - Schedule of Changes In Each Component of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Six months ended June 30,
Beginning Balance	$ 685,228	$ 619,241	$ 657,983	$ 600,764
Other comprehensive income	3,569	10,939	25,189	19,570
Ending balance	693,750	636,908	693,750	636,908
Defined Benefit Pension Plans
Six months ended June 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:
Six months ended June 30,
Beginning Balance	33,730	20	12,110	(8,611)
Other comprehensive income before reclassifications	3,565	10,956	24,036	19,654
Amounts reclassified from other comprehensive income	4	(17)	(44)	(84)
Reclassification of unrealized gains on held-to-maturity securities to available-for-sale			1,197
Other comprehensive income	3,569	10,939	25,189	19,570
Ending balance	37,299	10,959	37,299	10,959
Total
Six months ended June 30,
Beginning Balance	27,460	(5,851)	5,840	(14,482)
Other comprehensive income before reclassifications	3,565	10,956	24,036	19,654
Amounts reclassified from other comprehensive income	4	(17)	(44)	(84)
Reclassification of unrealized gains on held-to-maturity securities to available-for-sale			1,197
Other comprehensive income	3,569	10,939	25,189	19,570
Ending balance	$ 31,029	$ 5,088	$ 31,029	$ 5,088