Investment Securities Narrative (Details) (USD $)									6 Months Ended		3 Months Ended	6 Months Ended				6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Equity Securities [Member]	Dec. 31, 2012 Equity Securities [Member]	Jun. 30, 2013 Equity Securities Financial Institution [Member]	Dec. 31, 2012 Equity Securities Financial Institution [Member]	Jun. 30, 2013 Equity Securities, Other [Member]	Dec. 31, 2012 Equity Securities, Other [Member]	Jun. 30, 2013 Auction Rate Securities [Member]	Dec. 31, 2012 Auction Rate Securities [Member]	Jun. 30, 2013 Auction Rate Securities [Member] External Credit Rating, Rated Above Investment Grade [Member]	Jun. 30, 2013 Auction Rate Securities [Member] Moody's, A3 Rating [Member]	Jun. 30, 2013 Auction Rate Securities [Member] Moody's, A2 Rating [Member]	Jun. 30, 2013 Pooled Trust Preferred Securities [Member]	Jun. 30, 2013 Pooled Trust Preferred Securities [Member] External Credit Rating, Rated Below Investment Grade [Member]	Jun. 30, 2013 Single-issuer Trust Preferred Securities [Member]	Jun. 30, 2013 Single-issuer Trust Preferred Securities [Member] External Credit Rating, Rated Below Investment Grade [Member]	Jun. 30, 2013 Single-issuer Trust Preferred Securities [Member] External Credit Rating, BBB [Member]
Statement of Investments [Line Items]
Restricted equity securities issued by the Federal Home Loan Bank and Federal Reserve Bank			$ 95,300,000	$ 71,700,000
Available-for-sale Securities, Equity Securities					40,900,000	44,200,000	6,900,000	6,700,000
Amortized cost	2,933,939,000	2,752,220,000	136,364,000	118,465,000	34,300,000				172,092,000	174,026,000					3,800,000		20,800,000	4,700,000
Available for sale	2,915,652,000	2,793,725,000	143,119,000	122,563,000	40,900,000				152,592,000	149,339,000					5,400,000		19,500,000	3,700,000
SingleBankStockInvestment, cost basis	20,000,000
BankStockInvestmentFairValue	23,200,000
PercentOwnershipInAnIndividualFinancialInstitution	57.00%
IndividualBankStockInvestmentPercenttoTotalPortfolio	5.00%
Carrying Value Action Rate Securities Above Investment Grade											146,000,000
Percentage Action Rate Securities Above Investment Grade											95.00%
Carrying Value Auction Rate Securities Rated Investment Grade												8,000,000	100,000,000
Percentage Auction Rate Securities Investment Grade												5.00%	66.00%
Carrying value auction rate securities below investment grade									7,000,000
Percentage Auction Rate Securities Below Investment Grade									5.00%
US Government Guaranteed student loans below investment grade									5,000,000
Percentage US Government guaranteed student loans below investment grade									70.00%
US Government Guaranteed student loan auction rate securities									150,000,000
US Government Guaranteed student loan auction rate securities percentage									98.00%
Auction Rate Certificates Not Subject To Any Additional Other Than Temporary Impairment Charges Fair Value	152,600,000
Unrealized Gain (Loss) on Securities																(5,500,000)
Number of Trust Preferred Securities														8			7
Available-for-sale Securities, Amortized Cost Basis	2,933,939,000	2,752,220,000	136,364,000	118,465,000	34,300,000				172,092,000	174,026,000					3,800,000		20,800,000	4,700,000
Securities available for sale	2,915,652,000	2,793,725,000	143,119,000	122,563,000	40,900,000				152,592,000	149,339,000					5,400,000		19,500,000	3,700,000
Domestic Corporate debt securities	107,500,000
Available-for-sale Securities Pledged as Collateral	$ 1,700,000,000	$ 1,800,000,000