Shareholders' Equity - Changes in Balances of Component of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	$ 1,741,117	$ 1,660,702	$ 1,591,453
Other comprehensive income (loss) before reclassification	(32,971)	21,502	31,420
Amounts reclassified from accumulated other comprehensive income (loss)	1,462	1,047	659
Other comprehensive income (loss), net of tax amount	(31,509)	22,549	32,079
Balance	1,741,311	1,741,117	1,660,702
Securities Available for Sale and Transferred Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	17,331	(8,017)	(43,824)
Other comprehensive income (loss) before reclassification	(35,105)	25,348	35,807
Other comprehensive income (loss), net of tax amount	(35,105)	25,348	35,807
Balance	(17,774)	17,331	(8,017)
Defined Benefit Pension Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(18,382)	(15,583)	(12,324)
Other comprehensive income (loss) before reclassification	2,134	(3,846)	(4,278)
Amounts reclassified from accumulated other comprehensive income (loss)	1,462	1,047	1,019
Other comprehensive income (loss), net of tax amount	3,596	(2,799)	(3,259)
Balance	(14,786)	(18,382)	(15,583)
Cash Flow Hedge Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance			469
Other comprehensive income (loss) before reclassification			(109)
Amounts reclassified from accumulated other comprehensive income (loss)			(360)
Other comprehensive income (loss), net of tax amount			(469)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(1,051)	(23,600)	(55,679)
Balance	$ (32,560)	$ (1,051)	$ (23,600)