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, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal	$ 69,061	$ 73,278	$ 76,789
State	1,885	3,737	3,018
Total Current	70,946	77,015	79,807
Deferred:
Federal	6,947	(6,801)	(5,603)
State	240	284	392
Total Deferred	7,187	(6,517)	(5,211)
Provision for Income Taxes	78,133	70,498	74,596
Net tax charge/(benefit) recorded directly to consolidated shareholders' equity	7,900	1,000	$ 2,700
Deferred Tax Liabilities:
Accrued Pension Cost	(13,292)	(13,707)
Federal Home Loan Bank Stock	(5,088)	(5,088)
Lease Transactions	(87,454)	(85,874)
Energy Tax Credits	(10,476)	(8,054)
Net Unrealized Gains on Investments Securities	0	(3,453)
Investment in Variable Interest Entities	(1,883)	0
Deferred Loan Fees	(9,088)	(7,744)
Originated Mortgage Servicing Rights	(9,588)	(9,104)
Other	(691)	(657)
Gross Deferred Tax Liabilities	(137,560)	(133,681)
Deferred Tax Assets:
Accelerated Depreciation	6,027	7,775
Allowance for Loan Losses	43,705	42,890
Minimum Pension Liability	18,852	18,831
Accrued Expenses	18,693	16,738
Postretirement Benefit Obligations	12,900	12,849
Capital Lease Expenses	3,235	3,231
Restricted Stock	7,955	6,262
Net Unrealized Losses on Investment Securities	3,271	0
Investment in Variable Interest Entities	0	1,951
Deductible State and Local Taxes	3,956	4,166
Other	7,596	7,225
Gross Deferred Tax Assets Before Valuation Allowance	126,190	121,918
Valuation Allowance	(3,655)	(3,932)
Gross Deferred Tax Assets After Valuation Allowance	122,535	117,986
Net Deferred Tax Liabilities	(15,025)	$ (15,695)
Base year reserves included in retained earnings	18,200
Unrecognized deferred federal income tax liability	$ 7,200
Reconciliation of the Statutory Federal Income Tax Rate to the Company's Effective Tax Rate
Statutory Federal Income Tax Rate (as a percent)	35.00%	35.00%	35.00%
Increase (Decrease) in Income Tax Rate Resulting From:
State Taxes, Net of Federal Income Tax (as a percent)	0.60%	1.23%	0.59%
Tax Reserve Adjustments (as a percent)	(0.18%)	0.38%	0.88%
Leveraged Leases (as a percent)	(0.13%)	0.06%	0.01%
Low-Income Housing Investments (as a percent)	(0.69%)	(0.78%)	(0.10%)
Investment Tax Credits (as a percent)	(0.85%)	(0.89%)	(0.68%)
Bank-Owned Life Insurance (as a percent)	(0.88%)	(1.06%)	(0.97%)
Tax-Exempt Income (as a percent)	(2.71%)	(3.03%)	(2.83%)
Other (as a percent)	(0.06%)	(0.42%)	(0.51%)
Effective Tax Rate (as a percent)	30.10%	30.49%	31.39%