Fair Value Measurements Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Equity Securities [Member] | Level 1 [Member]
Available-for-sale Securities, Fair Value Disclosure	$ 34,983	$ 40,070
Equity Securities [Member] | Level 2 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Equity Securities [Member] | Level 3 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Equity Securities [Member] | Total [Member]
Available-for-sale Securities, Fair Value Disclosure	34,983	40,070
U.S. Government Securities [Member] | Level 1 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
U.S. Government Securities [Member] | Level 2 [Member]
Available-for-sale Securities, Fair Value Disclosure	1,325	1,649
U.S. Government Securities [Member] | Level 3 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
U.S. Government Securities [Member] | Total [Member]
Available-for-sale Securities, Fair Value Disclosure	1,325	1,649
State and Municipal Securities [Member] | Level 1 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
State and Municipal Securities [Member] | Level 2 [Member]
Available-for-sale Securities, Fair Value Disclosure	334,060	349,563
State and Municipal Securities [Member] | Level 3 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
State and Municipal Securities [Member] | Total [Member]
Available-for-sale Securities, Fair Value Disclosure	334,060	349,563
Corporate Debt Securities [Member] | Level 1 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Corporate Debt Securities [Member] | Level 2 [Member]
Available-for-sale Securities, Fair Value Disclosure	110,577	111,675
Corporate Debt Securities [Member] | Level 3 [Member]
Available-for-sale Securities, Fair Value Disclosure	11,858	13,111
Corporate Debt Securities [Member] | Total [Member]
Available-for-sale Securities, Fair Value Disclosure	122,435	124,786
Collateralized Mortgage Obligations [Member] | Level 1 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Collateralized Mortgage Obligations [Member] | Level 2 [Member]
Available-for-sale Securities, Fair Value Disclosure	1,107,255	1,104,058
Collateralized Mortgage Obligations [Member] | Level 3 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Collateralized Mortgage Obligations [Member] | Total [Member]
Available-for-sale Securities, Fair Value Disclosure	1,107,255	1,104,058
Mortgage-Backed Securities [Member] | Level 1 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Mortgage-Backed Securities [Member] | Level 2 [Member]
Available-for-sale Securities, Fair Value Disclosure	838,836	871,472
Mortgage-Backed Securities [Member] | Level 3 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Mortgage-Backed Securities [Member] | Total [Member]
Available-for-sale Securities, Fair Value Disclosure	838,836	871,472
Auction Rate Securities [Member] | Level 1 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Auction Rate Securities [Member] | Level 2 [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Auction Rate Securities [Member] | Level 3 [Member]
Available-for-sale Securities, Fair Value Disclosure	240,702	260,679
Auction Rate Securities [Member] | Total [Member]
Available-for-sale Securities, Fair Value Disclosure	240,702	260,679
Level 1 [Member]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Available-for-sale Securities, Fair Value Disclosure	34,983	40,070
Other Assets, Fair Value Disclosure	12,892	13,582
Assets, Fair Value Disclosure	47,875	53,652
Liabilities, Fair Value Disclosure	12,892	13,582
Level 1 [Member] | US Treasury and Government [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Level 2 [Member]
Mortgages Held-for-sale, Fair Value Disclosure	63,554	83,940
Available-for-sale Securities, Fair Value Disclosure	2,396,897	2,443,475
Other Assets, Fair Value Disclosure	6,952	9,256
Assets, Fair Value Disclosure	2,467,403	2,536,671
Liabilities, Fair Value Disclosure	5,669	760
Level 2 [Member] | US Treasury and Government [Member]
Available-for-sale Securities, Fair Value Disclosure	4,844	5,058
Level 3 [Member]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
Available-for-sale Securities, Fair Value Disclosure	252,560	273,790
Other Assets, Fair Value Disclosure	0	0
Assets, Fair Value Disclosure	252,560	273,790
Liabilities, Fair Value Disclosure	0	0
Level 3 [Member] | US Treasury and Government [Member]
Available-for-sale Securities, Fair Value Disclosure	0	0
Total [Member]
Mortgages Held-for-sale, Fair Value Disclosure	63,554	83,940
Available-for-sale Securities, Fair Value Disclosure	2,684,440	2,757,335
Other Assets, Fair Value Disclosure	19,844	22,838
Assets, Fair Value Disclosure	2,767,838	2,864,113
Liabilities, Fair Value Disclosure	18,561	14,342
Total [Member] | US Treasury and Government [Member]
Available-for-sale Securities, Fair Value Disclosure	$ 4,844	$ 5,058