Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investment securities available for sale:
Total investment securities available for sale	$ 4,926,758	$ 4,937,483
Trading assets	70,711	73,253
Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Total investment securities available for sale	3,845	12,701
Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Total investment securities available for sale	4,922,433	4,923,926
Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Total investment securities available for sale	480	856
Fair Value, Measurements, Recurring [Member]
Investment securities available for sale:
Total investment securities available for sale	4,926,758	4,937,483
Trading assets	82,125	80,647
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	80,110	89,591
Fair Value, Measurements, Recurring [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	1,004	1,001
Fair Value, Measurements, Recurring [Member] | Federal agency securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	24,049
Fair Value, Measurements, Recurring [Member] | Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Total investment securities available for sale	801,188	847,246
Fair Value, Measurements, Recurring [Member] | Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	3,804,304	3,785,590
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	228,166	18,543
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale		187,732
Fair Value, Measurements, Recurring [Member] | Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	92,096	73,322
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Total investment securities available for sale	3,845	12,701
Trading assets	0	0
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	1,004	1,001
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Federal agency securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	41
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	2,841	11,659
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Total investment securities available for sale	4,922,433	4,923,926
Trading assets	74,331	76,076
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	79,963	84,820
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Federal agency securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	24,008
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Total investment securities available for sale	801,188	847,246
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	3,804,304	3,785,590
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	228,166	18,543
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale		187,732
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	88,775	60,807
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Total investment securities available for sale	480	856
Trading assets	7,794	4,571
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	147	4,771
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Federal agency securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Mortgage Backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities [Member]
Investment securities available for sale:
Total investment securities available for sale		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	$ 480	$ 856