Investment Securities Narrative (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Statement of Investments [Line Items]
Amortized cost	$ 2,519,248,000	$ 2,608,210,000
Securities Available-for-sale	2,501,198,000	2,568,434,000
SingleBankStockInvestment, cost basis	20,000,000
BankStockInvestmentFairValue	27,900,000
PercentOwnershipInAnIndividualFinancialInstitution	70.10%
IndividualBankStockInvestmentPercenttoTotalPortfolio	5.00%
Proceeds from Sale of Available-for-sale Securities	11,900,000
Auction Rate Certificates Not Subject To Any Additional Other Than Temporary Impairment Charges Fair Value	147,700,000
Available-for-sale Securities, Amortized Cost Basis	2,519,248,000	2,608,210,000
Available-for-sale Securities	2,501,198,000	2,568,434,000
Domestic Corporate debt securities	100,600,000
Available-for-sale Securities Pledged as Collateral	1,800,000,000	0
Equity Securities [Member]
Statement of Investments [Line Items]
Amortized cost	34,231,000	33,922,000
Securities Available-for-sale	45,734,000	46,201,000
Available-for-sale Securities, Amortized Cost Basis	34,231,000	33,922,000
Available-for-sale Securities	45,734,000	46,201,000
Equity Securities Financial Institution [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Equity Securities	39,800,000	40,600,000
Amortized cost	28,500,000
Securities Available-for-sale	39,800,000
Available-for-sale Securities, Amortized Cost Basis	28,500,000
Available-for-sale Securities	39,800,000
Equity Securities, Other [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Equity Securities	5,900,000	5,600,000
Auction Rate Securities [Member]
Statement of Investments [Line Items]
Amortized cost	159,379,000	172,299,000
Securities Available-for-sale	147,713,000	159,274,000
Carrying value auction rate securities below investment grade	4,000,000
Percentage Auction Rate Securities Below Investment Grade	3.00%
US Government Guaranteed student loans below investment grade	3,000,000
Percentage US Government guaranteed student loans below investment grade	59.00%
US Government Guaranteed student loan auction rate securities	146,000,000
US Government Guaranteed student loan auction rate securities percentage	99.00%
Available-for-sale Securities, Amortized Cost Basis	159,379,000	172,299,000
Available-for-sale Securities	147,713,000	159,274,000
Pooled Trust Preferred Securities [Member]
Statement of Investments [Line Items]
Number of Trust Preferred Securities Below Investment Grade	8
Single-issuer Trust Preferred Securities [Member]
Statement of Investments [Line Items]
Unrealized Gain (Loss) on Securities	(5,600,000)
Number of Trust Preferred Securities Below Investment Grade	22
Moody's, A2 Rating [Member] | Auction Rate Securities [Member]
Statement of Investments [Line Items]
Carrying Value Auction Rate Securities Rated Investment Grade	103,000,000
Percentage Auction Rate Securities Investment Grade	70.00%
Moody's, A3 Rating [Member] | Auction Rate Securities [Member]
Statement of Investments [Line Items]
Carrying Value Auction Rate Securities Rated Investment Grade	6,000,000
Percentage Auction Rate Securities Investment Grade	4.00%
External Credit Rating, BBB [Member] | Single-issuer Trust Preferred Securities [Member]
Statement of Investments [Line Items]
Amortized cost	4,700,000
Securities Available-for-sale	3,800,000
Available-for-sale Securities, Amortized Cost Basis	4,700,000
Available-for-sale Securities	3,800,000
External Credit Rating, Rated Above Investment Grade [Member] | Auction Rate Securities [Member]
Statement of Investments [Line Items]
Carrying Value Action Rate Securities Above Investment Grade	143,000,000
Percentage Action Rate Securities Above Investment Grade	97.00%
External Credit Rating, Rated Below Investment Grade [Member] | Pooled Trust Preferred Securities [Member]
Statement of Investments [Line Items]
Amortized cost	2,800,000
Securities Available-for-sale	5,700,000
Available-for-sale Securities, Amortized Cost Basis	2,800,000
Available-for-sale Securities	5,700,000
External Credit Rating, Rated Below Investment Grade [Member] | Single-issuer Trust Preferred Securities [Member]
Statement of Investments [Line Items]
Amortized cost	13,500,000
Securities Available-for-sale	11,700,000
Number of Trust Preferred Securities Below Investment Grade	6
Available-for-sale Securities, Amortized Cost Basis	13,500,000
Available-for-sale Securities	$ 11,700,000