Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Investment securities available for sale:
Total investment securities available for sale	$ 4,669,100	$ 4,937,483
Derivatives (other assets)	1,133	2,079
Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Total investment securities available for sale	13,145	12,701
Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Total investment securities available for sale	4,655,354	4,923,926
Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Total investment securities available for sale	601	856
Fair Value, Measurements, Recurring [Member]
Investment securities available for sale:
Total investment securities available for sale	4,669,100	4,937,483
Derivatives (other assets)	79,857	80,647
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	81,328	89,591
Fair Value, Measurements, Recurring [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	1,001	1,001
Fair Value, Measurements, Recurring [Member] | Federal agency securities [Member]
Investment securities available for sale:
Total investment securities available for sale	8	24,049
Fair Value, Measurements, Recurring [Member] | Obligations of state and political subdivisions [Member]
Investment securities available for sale:
Total investment securities available for sale	835,664	847,246
Fair Value, Measurements, Recurring [Member] | Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	3,554,430	3,785,590
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	19,303	18,543
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member]
Investment securities available for sale:
Total investment securities available for sale	163,014	187,732
Fair Value, Measurements, Recurring [Member] | Other securities (debt and equity) [Member]
Investment securities available for sale:
Total investment securities available for sale	95,680	73,322
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Total investment securities available for sale	13,145	12,701
Derivatives (other 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	1,001	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	8	41
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Obligations of state and political subdivisions [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-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] | Asset-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] | Other securities (debt and equity) [Member]
Investment securities available for sale:
Total investment securities available for sale	12,136	11,659
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Total investment securities available for sale	4,655,354	4,923,926
Derivatives (other assets)	73,102	76,076
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	80,441	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 [Member]
Investment securities available for sale:
Total investment securities available for sale	835,664	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	3,554,430	3,785,590
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	19,303	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	163,014	187,732
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other securities (debt and equity) [Member]
Investment securities available for sale:
Total investment securities available for sale	82,943	60,807
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Total investment securities available for sale	601	856
Derivatives (other assets)	6,755	4,571
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	887	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 [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-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] | Asset-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] | Other securities (debt and equity) [Member]
Investment securities available for sale:
Total investment securities available for sale	$ 601	$ 856