Other Comprehensive Income (Loss) - Schedule of Activity in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning	$ 682,597	$ 647,267	$ 663,054	$ 620,871
Other comprehensive income	223	10,776	22,516	22,991
Balances at Ending	698,029	657,677	698,029	657,677
Cumulative Effect, Period Of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning			1,707
Available-for- Sale Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning	25,838	(11,695)	4,039	(23,589)
Other comprehensive income (loss) before reclassifications	(257)	10,676	21,866	22,570
Amounts reclassified from accumulated other comprehensive (loss) income	0	(204)	(324)	(204)
Other comprehensive income	(257)	10,472	21,542	22,366
Balances at Ending	25,581	(1,223)	25,581	(1,223)
Employee Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning	(47,109)	(39,255)	(47,603)	(39,576)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive (loss) income	480	304	974	625
Other comprehensive income	480	304	974	625
Balances at Ending	(46,629)	(38,951)	(46,629)	(38,951)
Accumulated Other Comprehensive (Loss) Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balances at Beginning	(21,271)	(50,950)	(43,564)	(63,165)
Other comprehensive income (loss) before reclassifications	(257)	10,676	21,866	22,570
Amounts reclassified from accumulated other comprehensive (loss) income	480	100	650	421
Other comprehensive income	223	10,776	22,516	22,991
Balances at Ending	$ (21,048)	$ (40,174)	$ (21,048)	$ (40,174)