Loans, Allowance for Credit Losses, and Credit Quality Commercial Loans by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Commercial loans by credit quality indicator
Commercial and industrial	$ 6,085,473	$ 5,905,902
Commercial real estate - owner occupied	966,689	1,007,937
Lease financing	42,607	51,529
Commercial and business lending	7,094,769	6,965,368
Commercial real estate - investor	3,183,352	3,056,485
Real estate construction	1,124,280	1,008,956
Commercial real estate lending	4,307,632	4,065,441
Total commercial	11,402,401	11,030,809
Pass [Member]
Commercial loans by credit quality indicator
Commercial and industrial	5,487,926	5,594,497
Commercial real estate - owner occupied	874,566	904,526
Lease financing	39,987	46,931
Commercial and business lending	6,402,479	6,545,954
Commercial real estate - investor	3,089,760	2,974,493
Real estate construction	1,120,173	998,972
Commercial real estate lending	4,209,933	3,973,465
Total commercial	10,612,412	10,519,419
Special Mention [Member]
Commercial loans by credit quality indicator
Commercial and industrial	318,587	119,328
Commercial real estate - owner occupied	29,946	18,437
Lease financing	624	88
Commercial and business lending	349,157	137,853
Commercial real estate - investor	44,458	12,137
Real estate construction	271	2,082
Commercial real estate lending	44,729	14,219
Total commercial	393,886	152,072
Potential Problem [Member]
Commercial loans by credit quality indicator
Commercial and industrial	191,941	108,522
Commercial real estate - owner occupied	41,466	48,695
Lease financing	233	2,709
Commercial and business lending	233,640	159,926
Commercial real estate - investor	23,633	24,043
Real estate construction	2,354	1,776
Commercial real estate lending	25,987	25,819
Total commercial	259,627	185,745
Impaired [Member]
Commercial loans by credit quality indicator
Commercial and industrial	87,019	83,555
Commercial real estate - owner occupied	20,711	36,279
Lease financing	1,763	1,801
Commercial and business lending	109,493	121,635
Commercial real estate - investor	25,501	45,812
Real estate construction	1,482	6,126
Commercial real estate lending	26,983	51,938
Total commercial	$ 136,476	$ 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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