Loans, Allowance for Loan Losses, and Credit Quality Commercial Loans by Credit Quality Indicator (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Commercial loans by credit quality indicator
Commercial and industrial	$ 4,703,056	$ 4,502,021
Commercial real estate - owner occupied	1,147,352	1,219,747
Lease financing	51,727	64,196
Commercial and business lending	5,902,135	5,785,964
Commercial real estate - investor	2,847,152	2,906,759
Real estate construction	834,744	655,381
Commercial real estate lending	3,681,896	3,562,140
Total commercial	9,584,031	9,348,104
Pass [Member]
Commercial loans by credit quality indicator
Commercial and industrial	4,359,412	4,208,478
Commercial real estate - owner occupied	988,166	1,030,632
Lease financing	50,176	58,099
Commercial and business lending	5,397,754	5,297,209
Commercial real estate - investor	2,617,045	2,634,035
Real estate construction	800,000	603,481
Commercial real estate lending	3,417,045	3,237,516
Total commercial	8,814,799	8,534,725
Special Mention [Member]
Commercial loans by credit quality indicator
Commercial and industrial	162,447	97,787
Commercial real estate - owner occupied	55,204	51,417
Lease financing	1,245	2,802
Commercial and business lending	218,896	152,006
Commercial real estate - investor	57,667	65,309
Real estate construction	3,709	6,976
Commercial real estate lending	61,376	72,285
Total commercial	280,272	224,291
Potential Problem [Member]
Commercial loans by credit quality indicator
Commercial and industrial	112,947	128,434
Commercial real estate - owner occupied	61,256	99,592
Lease financing	207	264
Commercial and business lending	174,410	228,290
Commercial real estate - investor	87,526	107,068
Real estate construction	7,540	13,092
Commercial real estate lending	95,066	120,160
Total commercial	269,476	348,450
Impaired [Member]
Commercial loans by credit quality indicator
Commercial and industrial	68,250	67,322
Commercial real estate - owner occupied	42,726	38,106
Lease financing	99	3,031
Commercial and business lending	111,075	108,459
Commercial real estate - investor	84,914	100,347
Real estate construction	23,495	31,832
Commercial real estate lending	108,409	132,179
Total commercial	$ 219,484	$ 240,638