Income Taxes (Deferred tax liabilities & assets and reconciliation of statutory federal income taxes to the company's effective tax rate) (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
Federal	$ 60,902	$ 45,464	$ 73,176
State	14,426	11,434	6,039
Total Current	75,328	56,898	79,215
Deferred:
Federal	(9,630)	(2,172)	5,042
State	(5,785)	(4,102)	(865)
Total Deferred	(15,415)	(6,274)	4,177
Provision for Income Taxes	59,913	50,624	83,392
Net tax charge/(benefit) recorded directly to consolidated shareholders' equity	7,100	3,200	$ 500
Deferred Tax Liabilities:
Accelerated Depreciation	4,064	2,864
Accrued Pension Cost	(11,270)	(11,270)
Federal Home Loan Bank Stock	(3,416)	(3,416)
Lease Transactions	(48,487)	(53,230)
Operating Lease Liabilities	(26,731)	0
Energy Tax Credits	(2,370)	(5,274)
Deferred Tax Liabilities, Unrealized Gains on Trading Securities	(2,751)	0
Deferred Tax Liabilities, Investment In Variable Interest Entities	(3,783)	(4,574)
Deferred Loan Fees	(6,498)	(6,688)
Originated Mortgage Servicing Rights	(6,840)	(6,548)
Other	(1,597)	(1,420)
Gross Deferred Tax Liabilities	(117,807)	(95,284)
Deferred Tax Assets:
Allowance for Loan Losses	30,951	30,045
Minimum Pension Liability	13,980	12,989
Accrued Expenses	18,159	14,805
Postretirement Benefit Obligations	8,130	8,396
Capital Lease Expenses	2,171	2,172
Restricted Stock	4,369	5,178
Operating Lease, Right-of-Use Asset	28,685	0
Deferred Tax Assets, Net Unrealized Losses on Investment Securities	0	5,421
Deductible State and Local Taxes	3,558	3,242
Qualified Affordable Housing Project Investments, Commitment Payments, Remainder of Fiscal Year	2,157	805
Other	6,236	4,244
Gross Deferred Tax Assets Before Valuation Allowance	118,396	87,297
Valuation Allowance	(2,460)	(1,102)
Gross Deferred Tax Assets After Valuation Allowance	115,936	86,195
Net Deferred Tax Liabilities	(1,871)	(9,089)
Tax Cuts and Jobs Act of 2017 additional tax expense		$ 3,600
Base year reserves included in retained earnings	18,200
Unrecognized deferred federal income tax liability	$ 4,800
Reconciliation of the Statutory Federal Income Tax Rate to the Company's Effective Tax Rate
Statutory Federal Income Tax Rate (as a percent)	21.00%	21.00%	35.00%
Increase (Decrease) in Income Tax Rate Resulting From:
State Taxes, Net of Federal Income Tax (as a percent)	2.53%	2.29%	1.50%
Tax Reserve Adjustments (as a percent)	(0.03%)	0.00%	0.04%
Leveraged Leases (as a percent)	0.60%	0.22%	(1.18%)
Low-Income Housing Investments (as a percent)	(0.84%)	(1.04%)	(1.03%)
Bank-Owned Life Insurance (as a percent)	(0.51%)	(0.55%)	(0.85%)
Tax-Exempt Income (as a percent)	(0.53%)	(1.29%)	(2.57%)
Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-based Payment Arrangement, Percent	0.22%	0.34%	0.83%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Leases, Percent	(1.54%)	(0.83%)	(0.03%)
Tax Reform Effects	0.00%	(0.75%)	1.25%
Other (as a percent)	0.50%	0.02%	(0.19%)
Effective Tax Rate (as a percent)	20.96%	18.73%	31.11%