Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Investment securities available for sale:
Total investment securities available for sale	$ 4,521,436	$ 4,937,483
Trading Assets	73,484	73,253
Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Total investment securities available for sale	6,627	12,701
Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Total investment securities available for sale	4,513,928	4,923,926
Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Total investment securities available for sale	881	856
Fair Value, Measurements, Recurring [Member]
Investment securities available for sale:
Total investment securities available for sale	4,521,436	4,937,483
Trading Assets	88,711	80,647
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	87,581	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	7	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	835,136	847,246
Fair Value, Measurements, Recurring [Member] | Residential mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	3,428,973	3,785,590
Fair Value, Measurements, Recurring [Member] | Commercial mortgage-related securities [Member]
Investment securities available for sale:
Total investment securities available for sale	21,407	18,543
Fair Value, Measurements, Recurring [Member] | Asset-backed securities [Member]
Investment securities available for sale:
Total investment securities available for sale	139,164	187,732
Fair Value, Measurements, Recurring [Member] | Other securities (debt and equity) [Member]
Investment securities available for sale:
Total investment securities available for sale	95,745	73,322
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Total investment securities available for sale	6,627	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	7	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	5,616	11,659
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Total investment securities available for sale	4,513,928	4,923,926
Trading Assets	77,519	76,076
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	84,660	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	835,136	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	3,428,973	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	21,407	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	139,164	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	89,248	60,807
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Total investment securities available for sale	881	856
Trading Assets	11,192	4,571
Liabilities, Fair Value Disclosure [Abstract]
Derivatives (other liabilities)	2,921	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	$ 881	$ 856