Investment Securities (Summary of Available for Sale Investment Securities by Maturity Groupings) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Amortized Cost	$ 7,557,474	$ 7,164,763
Fair Value	7,717,634	7,294,303
U.S. Government and Federal Agency Obligations [Member]
Amortized Cost	328,328	434,878
Fair Value	356,246	455,537
U.S. Government and Federal Agency Obligations [Member] | Available-for-Sale Securities, Maturity within 1 Year [Member]
Amortized Cost	2,365
Fair Value	2,367
U.S. Government and Federal Agency Obligations [Member] | Available-for-Sale Securities, Maturity After 1 But within 5 Years [Member]
Amortized Cost	135,522
Fair Value	147,445
U.S. Government and Federal Agency Obligations [Member] | Available-for-Sale securities, Maturity After 5 But within 10 Years [Member]
Amortized Cost	190,441
Fair Value	206,434
Government-Sponsored Enterprise Obligations [Member]
Amortized Cost	262,041	200,061
Fair Value	264,553	201,895
Government-Sponsored Enterprise Obligations [Member] | Available-for-Sale Securities, Maturity within 1 Year [Member]
Amortized Cost	85,130
Fair Value	86,384
Government-Sponsored Enterprise Obligations [Member] | Available-for-Sale Securities, Maturity After 1 But within 5 Years [Member]
Amortized Cost	107,184
Fair Value	108,351
Government-Sponsored Enterprise Obligations [Member] | Available-for-Sale securities, Maturity After 5 But within 10 Years [Member]
Amortized Cost	58,727
Fair Value	58,863
Government-Sponsored Enterprise Obligations [Member] | Available-for-Sale, Maturity After 10 Years [Member]
Amortized Cost	11,000
Fair Value	10,955
State and Municipal Obligations [Member]
Amortized Cost	1,184,795	1,117,020
Fair Value	1,193,561	1,119,485
State and Municipal Obligations [Member] | Available-for-Sale Securities, Maturity within 1 Year [Member]
Amortized Cost	135,296
Fair Value	136,620
State and Municipal Obligations [Member] | Available-for-Sale Securities, Maturity After 1 But within 5 Years [Member]
Amortized Cost	459,340
Fair Value	472,245
State and Municipal Obligations [Member] | Available-for-Sale securities, Maturity After 5 But within 10 Years [Member]
Amortized Cost	355,389
Fair Value	357,330
State and Municipal Obligations [Member] | Available-for-Sale, Maturity After 10 Years [Member]
Amortized Cost	234,770
Fair Value	227,366
Mortgage and Asset-Backed Securities [Member] | Agency Mortgage-Backed Securities [Member]
Amortized Cost	2,845,564
Fair Value	2,913,805
Mortgage and Asset-Backed Securities [Member] | Non-Agency Mortgage-Backed Securities [Member]
Amortized Cost	383,271
Fair Value	385,937
Mortgage and Asset-Backed Securities [Member] | Other Asset-Backed Securities [Member]
Amortized Cost	2,383,208
Fair Value	2,394,627
Other Debt Securities [Member]
Amortized Cost	159,976	165,883
Fair Value	168,859	176,964
Other Debt Securities [Member] | Available-for-Sale Securities, Maturity within 1 Year [Member]
Amortized Cost	61,531
Fair Value	62,499
Other Debt Securities [Member] | Available-for-Sale Securities, Maturity After 1 But within 5 Years [Member]
Amortized Cost	98,445
Fair Value	106,360
Equity Securities [Member]
Amortized Cost	10,291	7,569
Fair Value	40,046	39,173
Agency Mortgage-Backed Securities [Member]
Amortized Cost	2,845,564	2,437,123
Fair Value	2,913,805	2,491,199
Non-Agency Mortgage-Backed Securities [Member]
Amortized Cost	383,271	459,363
Fair Value	385,937	455,790
Total Mortgage and Asset-Backed Securities [Member]
Amortized Cost	5,612,043	5,239,352
Fair Value	$ 5,694,369	$ 5,301,249