Income Taxes - Schedule of Significant Components of the Company's Deferred Tax Liabilities and Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Liabilities:
Accelerated Depreciation	$ (8,042)	$ (4,064)
Accrued Pension Cost	(11,270)	(11,270)
Federal Home Loan Bank Stock	(3,416)	(3,416)
Lease Transactions	(41,726)	(48,487)
Operating Lease Right-of-Use Assets	(26,387)	(26,731)
Energy Tax Credits	(674)	(2,370)
Net Unrealized Gains on Investments Securities	(18,407)	(2,751)
Investment in Variable Interest Entities	(2,725)	(3,783)
Deferred Loan Fees	(4,736)	(6,498)
Originated Mortgage Servicing Rights	(5,579)	(6,840)
Other	(1,124)	(1,597)
Gross Deferred Tax Liabilities	(124,086)	(117,807)
Deferred Tax Assets:
Allowance for Credit Losses	57,840	30,951
Minimum Pension Liability	13,430	13,980
Accrued Expenses	17,629	18,159
Postretirement Benefit Obligations	7,980	8,130
Capital Lease Expenses	2,168	2,171
Operating Lease Liabilities	28,473	28,685
Restricted Stock	3,669	4,369
Deductible State and Local Taxes	3,366	3,558
Low Income Housing Investments	3,648	2,157
Other	6,204	6,236
Gross Deferred Tax Assets Before Valuation Allowance	144,407	118,396
Valuation Allowance	(3,597)	(2,460)
Gross Deferred Tax Assets After Valuation Allowance	140,810	115,936
Net Deferred Tax Assets (Liabilities)	$ 16,724
Net Deferred Tax Assets (Liabilities)		$ (1,871)