Loans, Allowance for Loan Losses, and Credit Quality Commercial Loans by Credit Quality Indicator (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commercial loans by credit quality indicator
Commercial and industrial	$ 5,603,899	$ 4,822,680
Commercial real estate - owner occupied	1,014,335	1,114,715
Lease financing	52,600	55,483
Commercial and business lending	6,670,834	5,992,878
Commercial real estate - investor	3,043,361	2,939,456
Real estate construction	982,426	896,248
Commercial real estate lending	4,025,787	3,835,704
Total commercial	10,696,621	9,828,582
Pass [Member]
Commercial loans by credit quality indicator
Commercial and industrial	5,268,521	4,485,160
Commercial real estate - owner occupied	900,306	959,849
Lease financing	45,506	52,733
Commercial and business lending	6,214,333	5,497,742
Commercial real estate - investor	2,930,817	2,740,255
Real estate construction	967,914	877,911
Commercial real estate lending	3,898,731	3,618,166
Total commercial	10,113,064	9,115,908
Special Mention [Member]
Commercial loans by credit quality indicator
Commercial and industrial	113,864	153,615
Commercial real estate - owner occupied	29,107	55,404
Lease financing	1,360	897
Commercial and business lending	144,331	209,916
Commercial real estate - investor	34,524	64,230
Real estate construction	3,293	2,814
Commercial real estate lending	37,817	67,044
Total commercial	182,148	276,960
Potential Problem [Member]
Commercial loans by credit quality indicator
Commercial and industrial	133,416	113,669
Commercial real estate - owner occupied	49,008	56,789
Lease financing	3,787	1,784
Commercial and business lending	186,211	172,242
Commercial real estate - investor	28,474	52,429
Real estate construction	2,227	5,263
Commercial real estate lending	30,701	57,692
Total commercial	216,912	229,934
Impaired [Member]
Commercial loans by credit quality indicator
Commercial and industrial	88,098	70,236
Commercial real estate - owner occupied	35,914	42,673
Lease financing	1,947	69
Commercial and business lending	125,959	112,978
Commercial real estate - investor	49,546	82,542
Real estate construction	8,992	10,260
Commercial real estate lending	58,538	92,802
Total commercial	$ 184,497	$ 205,780