Fair Value Measurements (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Investment securities available for sale:
Total investment securities available for sale	$ 5,742,034	$ 6,101,341
Derivatives (other assets)	2,100	1,530
Fair Value, Measurements, Recurring [Member]
Investment securities available for sale:
Total investment securities available for sale	5,742,034	6,101,341
Derivatives (other assets)	58,197	61,301
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	68,606	66,294
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Total investment securities available for sale	14,064	13,261
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	1,106	1,208
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	47	51
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	12,911	12,002
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Total investment securities available for sale	5,726,330	6,086,408
Derivatives (other assets)	56,889	55,684
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	68,440	66,216
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	27,145	29,716
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	818,212	838,602
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	4,578,387	4,910,497
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	13,050	7,753
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	243,115	298,841
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	46,421	999
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Total investment securities available for sale	1,640	1,672
Derivatives (other assets)	1,308	5,617
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	166	78
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	1,640	1,672
Fair Value, Measurements, Recurring [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Total investment securities available for sale	1,106	1,208
Fair Value, Measurements, Recurring [Member] | Federal agency securities [Member]
Investment securities available for sale:
Total investment securities available for sale	27,192	29,767
Fair Value, Measurements, Recurring [Member] | Obligations of state and political subdivisions [Member]
Investment securities available for sale:
Total investment securities available for sale	818,212	838,602
Fair Value, Measurements, Recurring [Member] | Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	4,578,387	4,910,497
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	13,050	7,753
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member]
Investment securities available for sale:
Total investment securities available for sale	243,115	298,841
Fair Value, Measurements, Recurring [Member] | Other securities (debt and equity) [Member]
Investment securities available for sale:
Total investment securities available for sale	$ 60,972	$ 14,673