Investment Securities Narrative (Details) (USD $)										3 Months Ended		3 Months Ended					3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Mar. 31, 2013 Equity Securities [Member]	Dec. 31, 2012 Equity Securities [Member]	Mar. 31, 2013 Equity Securities Financial Institution [Member]	Dec. 31, 2012 Equity Securities Financial Institution [Member]	Mar. 31, 2013 Equity Securities, Other [Member]	Dec. 31, 2012 Equity Securities, Other [Member]	Mar. 31, 2013 Auction Rate Securities [Member]	Dec. 31, 2012 Auction Rate Securities [Member]	Mar. 31, 2013 Auction Rate Securities [Member] External Credit Rating, Rated Above Investment Grade [Member]	Mar. 31, 2013 Auction Rate Securities [Member] Moody's, A3 Rating [Member]	Mar. 31, 2013 Auction Rate Securities [Member] Moody's, A2 Rating [Member]	Mar. 31, 2013 Pooled Trust Preferred Securities [Member]	Mar. 31, 2013 Pooled Trust Preferred Securities [Member] External Credit Rating, Rated Below Investment Grade [Member]	Mar. 31, 2013 Single-issuer Trust Preferred Securities [Member]	Mar. 31, 2013 Single-issuer Trust Preferred Securities [Member] External Credit Rating, Rated Below Investment Grade [Member]	Mar. 31, 2013 Single-issuer Trust Preferred Securities [Member] External Credit Rating, BBB [Member]
Statement of Investments [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	$ 23,100,000		$ 22,800,000
Restricted equity securities issued by the Federal Home Loan Bank and Federal Reserve Bank				74,500,000	71,700,000
Available-for-sale Securities, Equity Securities						42,500,000	44,200,000	6,900,000	6,700,000
Amortized cost	2,770,956,000	2,752,220,000		117,624,000	118,465,000	36,400,000				173,966,000	174,026,000					5,400,000		22,900,000	4,700,000
Available for sale	2,811,847,000	2,793,725,000		123,890,000	122,563,000	42,500,000				154,639,000	149,339,000					8,200,000		22,700,000	3,400,000
SingleBankStockInvestment, cost basis	20,000,000
BankStockInvestmentFairValue	22,600,000
PercentOwnershipInAnIndividualFinancialInstitution	50.00%
IndividualBankStockInvestmentPercenttoTotalPortfolio	5.00%
Carrying Value Action Rate Securities Above Investment Grade												143,000,000
Percentage Action Rate Securities Above Investment Grade												92.00%
Carrying Value Auction Rate Securities Rated Investment Grade													8,000,000	100,000,000
Percentage Auction Rate Securities Investment Grade													5.00%	65.00%
Carrying value auction rate securities below investment grade										12,000,000
Percentage Auction Rate Securities Below Investment Grade										8.00%
US Government Guaranteed student loans below investment grade										8,000,000
Percentage US Government guaranteed student loans below investment grade										72.00%
US Government Guaranteed student loan auction rate securities										151,000,000
US Government Guaranteed student loan auction rate securities percentage										97.00%
Auction Rate Certificates Not Subject To Any Additional Other Than Temporary Impairment Charges Fair Value	154,600,000
Unrealized Gain (Loss) on Securities																	(4,300,000)
Number of Trust Preferred Securities															10	9		8
Available-for-sale Securities, Amortized Cost Basis	2,770,956,000	2,752,220,000		117,624,000	118,465,000	36,400,000				173,966,000	174,026,000					5,400,000		22,900,000	4,700,000
Securities available for sale	2,811,847,000	2,793,725,000		123,890,000	122,563,000	42,500,000				154,639,000	149,339,000					8,200,000		22,700,000	3,400,000
Domestic Corporate debt securities	115,000,000
Available-for-sale Securities Pledged as Collateral	$ 1,800,000,000	$ 0