Fair Value Measurements Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Available-for-sale Securities, Fair Value Disclosure	$ 2,501,198	$ 2,568,434
Equity Securities [Member]
Available-for-sale Securities, Fair Value Disclosure	45,734	46,201
U.S. Government Securities [Member]
Available-for-sale Securities, Fair Value Disclosure	526	525
U.S. Government-Sponsored Agency Securities [Member]
Available-for-sale Securities, Fair Value Disclosure	280	726
State and Municipal Securities [Member]
Available-for-sale Securities, Fair Value Disclosure	283,453	284,849
Corporate Debt Securities [Member]
Available-for-sale Securities, Fair Value Disclosure	100,552	98,749
Collateralized Mortgage Obligations [Member]
Available-for-sale Securities, Fair Value Disclosure	1,006,737	1,032,398
Mortgage-Backed Securities [Member]
Available-for-sale Securities, Fair Value Disclosure		945,712
Auction Rate Securities [Member]
Available-for-sale Securities, Fair Value Disclosure	147,713	159,274
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Available-for-sale Securities, Fair Value Disclosure	45,734	46,201
Other Assets, Fair Value Disclosure	15,943	15,779
Assets, Fair Value Disclosure	61,677	61,980
Liabilities, Fair Value Disclosure	15,886	15,648
Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	45,734	46,201
Fair Value, Inputs, Level 1 [Member] | U.S. Government Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | State and Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 1 [Member] | Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Mortgages Held-for-sale, Fair Value Disclosure	24,417	21,351
Available-for-sale Securities, Fair Value Disclosure	2,298,272	2,353,872
Other Assets, Fair Value Disclosure	7,798	7,227
Assets, Fair Value Disclosure	2,330,487	2,382,450
Liabilities, Fair Value Disclosure	6,841	5,161
Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2 [Member] | U.S. Government Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	526	525
Fair Value, Inputs, Level 2 [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	280	726
Fair Value, Inputs, Level 2 [Member] | State and Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	283,453	284,849
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	91,073	89,662
Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	1,006,737	1,032,398
Fair Value, Inputs, Level 2 [Member] | Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	916,203	945,712
Fair Value, Inputs, Level 2 [Member] | Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Available-for-sale Securities, Fair Value Disclosure	157,192	168,361
Other Assets, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	157,192	168,361
Liabilities, Fair Value Disclosure	0	0
Level 3 [Member] | Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Level 3 [Member] | U.S. Government Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Level 3 [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Level 3 [Member] | State and Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Level 3 [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	9,479	9,087
Level 3 [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Level 3 [Member] | Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Level 3 [Member] | Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	147,713	159,274
Total [Member] | Fair Value, Measurements, Recurring [Member]
Mortgages Held-for-sale, Fair Value Disclosure	24,417	21,351
Available-for-sale Securities, Fair Value Disclosure	2,501,198	2,568,434
Other Assets, Fair Value Disclosure	23,741	23,006
Assets, Fair Value Disclosure	2,549,356	2,612,791
Liabilities, Fair Value Disclosure	22,727	20,809
Total [Member] | Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	45,734	46,201
Total [Member] | U.S. Government Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	526	525
Total [Member] | U.S. Government-Sponsored Agency Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	280	726
Total [Member] | State and Municipal Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	283,453	284,849
Total [Member] | Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	100,552	98,749
Total [Member] | Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	1,006,737	1,032,398
Total [Member] | Mortgage-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	916,203	945,712
Total [Member] | Auction Rate Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities, Fair Value Disclosure	$ 147,713	$ 159,274