Loans, Allowance for Loan Losses, and Credit Quality Commercial Loans by Credit Quality Indicator (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Commercial loans by credit quality indicator
Commercial and industrial	$ 5,905,902	$ 4,822,680
Commercial real estate - owner occupied	1,007,937	1,114,715
Lease financing	51,529	55,483
Commercial and business lending	6,965,368	5,992,878
Commercial real estate - investor	3,056,485	2,939,456
Real estate construction	1,008,956	896,248
Commercial real estate lending	4,065,441	3,835,704
Total commercial	11,030,809	9,828,582
Pass [Member]
Commercial loans by credit quality indicator
Commercial and industrial	5,594,497	4,485,160
Commercial real estate - owner occupied	904,526	959,849
Lease financing	46,931	52,733
Commercial and business lending	6,545,954	5,497,742
Commercial real estate - investor	2,974,493	2,740,255
Real estate construction	998,972	877,911
Commercial real estate lending	3,973,465	3,618,166
Total commercial	10,519,419	9,115,908
Special Mention [Member]
Commercial loans by credit quality indicator
Commercial and industrial	119,328	153,615
Commercial real estate - owner occupied	18,437	55,404
Lease financing	88	897
Commercial and business lending	137,853	209,916
Commercial real estate - investor	12,137	64,230
Real estate construction	2,082	2,814
Commercial real estate lending	14,219	67,044
Total commercial	152,072	276,960
Potential Problem [Member]
Commercial loans by credit quality indicator
Commercial and industrial	108,522	113,669
Commercial real estate - owner occupied	48,695	56,789
Lease financing	2,709	1,784
Commercial and business lending	159,926	172,242
Commercial real estate - investor	24,043	52,429
Real estate construction	1,776	5,263
Commercial real estate lending	25,819	57,692
Total commercial	185,745	229,934
Impaired [Member]
Commercial loans by credit quality indicator
Commercial and industrial	83,555	70,236
Commercial real estate - owner occupied	36,279	42,673
Lease financing	1,801	69
Commercial and business lending	121,635	112,978
Commercial real estate - investor	45,812	82,542
Real estate construction	6,126	10,260
Commercial real estate lending	51,938	92,802
Total commercial	$ 173,573	$ 205,780

Commercial and business lending subtotal

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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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