Loans, Allowance for Loan Losses, and Credit Quality Commercial Loans by Credit Quality Indicator (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Commercial loans by credit quality indicator
Commercial and industrial	$ 5,222,141	$ 4,822,680
Commercial real estate - owner occupied	1,098,089	1,114,715
Lease financing	52,500	55,483
Commercial and business lending	6,372,730	5,992,878
Commercial real estate - investor	3,001,219	2,939,456
Real estate construction	969,617	896,248
Commercial real estate lending	3,970,836	3,835,704
Total commercial	10,343,566	9,828,582
Pass [Member]
Commercial loans by credit quality indicator
Commercial and industrial	4,923,304	4,485,160
Commercial real estate - owner occupied	938,769	959,849
Lease financing	46,892	52,733
Commercial and business lending	5,908,965	5,497,742
Commercial real estate - investor	2,835,903	2,740,255
Real estate construction	951,759	877,911
Commercial real estate lending	3,787,662	3,618,166
Total commercial	9,696,627	9,115,908
Special Mention [Member]
Commercial loans by credit quality indicator
Commercial and industrial	123,546	153,615
Commercial real estate - owner occupied	56,221	55,404
Lease financing	2,371	897
Commercial and business lending	182,138	209,916
Commercial real estate - investor	50,895	64,230
Real estate construction	3,367	2,814
Commercial real estate lending	54,262	67,044
Total commercial	236,400	276,960
Potential Problem [Member]
Commercial loans by credit quality indicator
Commercial and industrial	109,027	113,669
Commercial real estate - owner occupied	64,785	56,789
Lease financing	3,065	1,784
Commercial and business lending	176,877	172,242
Commercial real estate - investor	34,790	52,429
Real estate construction	4,870	5,263
Commercial real estate lending	39,660	57,692
Total commercial	216,537	229,934
Impaired [Member]
Commercial loans by credit quality indicator
Commercial and industrial	66,264	70,236
Commercial real estate - owner occupied	38,314	42,673
Lease financing	172	69
Commercial and business lending	104,750	112,978
Commercial real estate - investor	79,631	82,542
Real estate construction	9,621	10,260
Commercial real estate lending	89,252	92,802
Total commercial	$ 194,002	$ 205,780