Fair Value Measurements Asset and Liabilities Measured at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investment securities available for sale:
Investment securities available for sale, fair value	$ 5,345,422	$ 5,250,585
Trading assets	34,005	43,728
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	36,003	46,470
Fair Value, Inputs, Level 3 [Member] | Federal agency securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0
Fair Value, Measurements, Recurring [Member]
Investment securities available for sale:
Trading assets	42,388	52,773
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	43,569	53,798
Fair Value, Measurements, Recurring [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	996	1,002
Fair Value, Measurements, Recurring [Member] | Federal agency securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Obligations of state and political subdivisions (municipal securities) [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	614,436	676,080
Fair Value, Measurements, Recurring [Member] | Government-Sponsored Enterprise (GSE) [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	3,741,040	3,838,430
Fair Value, Measurements, Recurring [Member] | Private Label [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	2,482	3,014
Fair Value, Measurements, Recurring [Member] | GNMA commercial mortgage-related securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	980,602	647,477
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value		23,059
Fair Value, Measurements, Recurring [Member] | Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	5,866	61,523
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	3,662	4,240
Trading assets	0	0
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	996	1,002
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Federal agency securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
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:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Government-Sponsored Enterprise (GSE) [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Private Label [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | GNMA commercial mortgage-related securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	2,666	3,238
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	5,341,560	5,246,046
Trading assets	40,948	51,056
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	42,946	53,798
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Federal agency securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
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:
Investment securities available for sale, fair value	614,436	676,080
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Government-Sponsored Enterprise (GSE) [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	3,741,040	3,838,430
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Private Label [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	2,482	3,014
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | GNMA commercial mortgage-related securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	980,602	647,477
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value		23,059
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	3,000	57,986
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	200	299
Trading assets	1,440	1,717
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	623	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Federal agency securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value		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:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Government-Sponsored Enterprise (GSE) [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Private Label [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | GNMA commercial mortgage-related securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Debt And Other Equity Securities [Member]
Investment securities available for sale:
Investment securities available for sale, fair value	$ 200	$ 299