Investment Securities Narrative (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Statement of Investments [Line Items]
Gain (Loss) on Sale of Securities, Net	$ 1,124,000	$ 2,892,000	$ 1,124,000	$ 5,365,000
Amortized cost	2,496,457,000		2,496,457,000		2,608,210,000
Securities Available-for-sale	2,497,776,000		2,497,776,000		2,568,434,000
SingleBankStockInvestment, cost basis	20,000,000		20,000,000
BankStockInvestmentFairValue	28,200,000		28,200,000
PercentOwnershipInAnIndividualFinancialInstitution	70.20%		70.20%
IndividualBankStockInvestmentPercenttoTotalPortfolio	5.00%		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	146,900,000		146,900,000
Available-for-sale Securities, Amortized Cost Basis	2,496,457,000		2,496,457,000		2,608,210,000
Available-for-sale Securities	2,497,776,000		2,497,776,000		2,568,434,000
Domestic Corporate debt securities	100,700,000		100,700,000
Available-for-sale Securities Pledged as Collateral	1,800,000,000		1,800,000,000		1,700,000,000
Equity Securities [Member]
Statement of Investments [Line Items]
Amortized cost	34,275,000		34,275,000		33,922,000
Securities Available-for-sale	46,248,000		46,248,000		46,201,000
Available-for-sale Securities, Amortized Cost Basis	34,275,000		34,275,000		33,922,000
Available-for-sale Securities	46,248,000		46,248,000		46,201,000
Equity Securities Financial Institution [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Equity Securities	40,200,000		40,200,000		40,600,000
Amortized cost	28,500,000		28,500,000
Securities Available-for-sale	40,200,000		40,200,000
Available-for-sale Securities, Amortized Cost Basis	28,500,000		28,500,000
Available-for-sale Securities	40,200,000		40,200,000
Equity Securities, Other [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Equity Securities	6,000,000		6,000,000		5,600,000
Auction Rate Securities [Member]
Statement of Investments [Line Items]
Amortized cost	158,463,000		158,463,000		172,299,000
Securities Available-for-sale	146,931,000		146,931,000		159,274,000
Carrying value auction rate securities below investment grade	4,000,000		4,000,000
Percentage Auction Rate Securities Below Investment Grade	3.00%		3.00%
US Government Guaranteed student loans below investment grade	3,000,000		3,000,000
Percentage US Government guaranteed student loans below investment grade	59.00%		59.00%
US Government Guaranteed student loan auction rate securities	145,000,000		145,000,000
US Government Guaranteed student loan auction rate securities percentage			99.00%
Available-for-sale Securities, Amortized Cost Basis	158,463,000		158,463,000		172,299,000
Available-for-sale Securities	146,931,000		146,931,000		159,274,000
Pooled Trust Preferred Securities [Member]
Statement of Investments [Line Items]
Number of Securities Sold	2		2
Available-for-sale Securities, Gross Realized Gains (Losses), Cost Basis of Securities Sold	728,000		728,000
Gain (Loss) on Sale of Securities, Net	1,100,000		1,100,000
Number of Trust Preferred Securities Below Investment Grade	6		6
Single-issuer Trust Preferred Securities [Member]
Statement of Investments [Line Items]
Unrealized Gain (Loss) on Securities			(4,300,000)
Number of Trust Preferred Securities Below Investment Grade	20		20
Moody's, A2 Rating [Member] | Auction Rate Securities [Member]
Statement of Investments [Line Items]
Carrying Value Auction Rate Securities Rated Investment Grade	102,000,000		102,000,000
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		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		4,700,000
Securities Available-for-sale	3,800,000		3,800,000
Available-for-sale Securities, Amortized Cost Basis	4,700,000		4,700,000
Available-for-sale Securities	3,800,000		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	2,100,000		2,100,000
Securities Available-for-sale	4,300,000		4,300,000
Available-for-sale Securities, Amortized Cost Basis	2,100,000		2,100,000
Available-for-sale Securities	4,300,000		4,300,000
External Credit Rating, Rated Below Investment Grade [Member] | Single-issuer Trust Preferred Securities [Member]
Statement of Investments [Line Items]
Amortized cost	13,500,000		13,500,000
Securities Available-for-sale	12,100,000		12,100,000
Number of Trust Preferred Securities Below Investment Grade	6		6
Available-for-sale Securities, Amortized Cost Basis	13,500,000		13,500,000
Available-for-sale Securities	$ 12,100,000		$ 12,100,000