Loans, Allowance for Credit Losses, and Credit Quality Commercial Loans by Credit Quality Indicator (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Commercial loans by credit quality indicator
Commercial and industrial	$ 6,140,420	$ 5,905,902
Commercial real estate - owner occupied	1,003,885	1,007,937
Lease financing	49,496	51,529
Commercial and business lending	7,193,801	6,965,368
Commercial real estate - investor	3,086,980	3,056,485
Real estate construction	1,019,571	1,008,956
Commercial real estate lending	4,106,551	4,065,441
Total commercial	11,300,352	11,030,809
Pass [Member]
Commercial loans by credit quality indicator
Commercial and industrial	5,820,038	5,594,497
Commercial real estate - owner occupied	911,673	904,526
Lease financing	44,857	46,931
Commercial and business lending	6,776,568	6,545,954
Commercial real estate - investor	3,013,499	2,974,493
Real estate construction	1,011,271	998,972
Commercial real estate lending	4,024,770	3,973,465
Total commercial	10,801,338	10,519,419
Special Mention [Member]
Commercial loans by credit quality indicator
Commercial and industrial	93,893	119,328
Commercial real estate - owner occupied	17,457	18,437
Lease financing	910	88
Commercial and business lending	112,260	137,853
Commercial real estate - investor	10,938	12,137
Real estate construction	673	2,082
Commercial real estate lending	11,611	14,219
Total commercial	123,871	152,072
Potential Problem [Member]
Commercial loans by credit quality indicator
Commercial and industrial	138,403	108,522
Commercial real estate - owner occupied	43,114	48,695
Lease financing	2,009	2,709
Commercial and business lending	183,526	159,926
Commercial real estate - investor	26,026	24,043
Real estate construction	1,487	1,776
Commercial real estate lending	27,513	25,819
Total commercial	211,039	185,745
Impaired [Member]
Commercial loans by credit quality indicator
Commercial and industrial	88,086	83,555
Commercial real estate - owner occupied	31,641	36,279
Lease financing	1,720	1,801
Commercial and business lending	121,447	121,635
Commercial real estate - investor	36,517	45,812
Real estate construction	6,140	6,126
Commercial real estate lending	42,657	51,938
Total commercial	$ 164,104	$ 173,573

Commercial and business lending subtotal

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Commercial Real Estate Investor loans receivable.

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Amount before allowance of commercial leases and leveraged lease transactions where the entity is long-term creditor. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes leases covered under loss sharing agreements.

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Amount before allowance of commercial loans and leases receivable includes, but not limited to, commercial and industrial loans, agricultural loans, mortgage loans, promissory notes, interbank and other loans to financial institutions, draws against credit facilities, trade financing, lease financings. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Amount before allowance of loans issued to commercial and industrial institutions. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes real estate loans and loans covered under loss sharing agreements.

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Amount before allowance of commercial construction loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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Amount before allowance of commercial loans issued to businesses to acquire, develop, construct, improve, or refinance land or building. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans covered under loss sharing agreements.

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