Loans, Allowance for Credit Losses, and Credit Quality Commercial Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Commercial loans by credit quality indicator
Commercial and industrial	$ 6,208,192	$ 5,905,902
Commercial real estate - owner occupied	978,183	1,007,937
Lease financing	46,900	51,529
Commercial and business lending	7,233,275	6,965,368
Commercial real estate - investor	3,126,440	3,056,485
Real estate construction	1,092,308	1,008,956
Commercial real estate lending	4,218,748	4,065,441
Total commercial	11,452,023	11,030,809
Pass [Member]
Commercial loans by credit quality indicator
Commercial and industrial	5,753,506	5,594,497
Commercial real estate - owner occupied	886,336	904,526
Lease financing	39,549	46,931
Commercial and business lending	6,679,391	6,545,954
Commercial real estate - investor	3,060,371	2,974,493
Real estate construction	1,086,630	998,972
Commercial real estate lending	4,147,001	3,973,465
Total commercial	10,826,392	10,519,419
Special Mention [Member]
Commercial loans by credit quality indicator
Commercial and industrial	232,242	119,328
Commercial real estate - owner occupied	25,596	18,437
Lease financing	4,310	88
Commercial and business lending	262,148	137,853
Commercial real estate - investor	14,427	12,137
Real estate construction	731	2,082
Commercial real estate lending	15,158	14,219
Total commercial	277,306	152,072
Potential Problem [Member]
Commercial loans by credit quality indicator
Commercial and industrial	125,643	108,522
Commercial real estate - owner occupied	41,997	48,695
Lease financing	1,385	2,709
Commercial and business lending	169,025	159,926
Commercial real estate - investor	23,543	24,043
Real estate construction	1,327	1,776
Commercial real estate lending	24,870	25,819
Total commercial	193,895	185,745
Impaired [Member]
Commercial loans by credit quality indicator
Commercial and industrial	96,801	83,555
Commercial real estate - owner occupied	24,254	36,279
Lease financing	1,656	1,801
Commercial and business lending	122,711	121,635
Commercial real estate - investor	28,099	45,812
Real estate construction	3,620	6,126
Commercial real estate lending	31,719	51,938
Total commercial	$ 154,430	$ 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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