Balance Sheet Offsetting (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Liabilities:
Repurchase Agreements, Gross Amounts of Recognized Liabilities	$ 797,213,000	$ 770,049,000
Repurchase Agreements, Gross Amounts Offset in the Statements of Condition	0	0
Repurchase Agreements, Net Amounts of Liabilities Presented in the Statements of Condition	797,213,000	770,049,000
Repurchase Agreements,Collateral, Right to Reclaim Securities	797,213,000	770,049,000
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral	0	0
Government entity deposits	1,300,000,000	1,200,000,000
Interest Rate Swap Agreements
Offsetting Assets and Liabilities [Line items]
Net liability positions, aggregate fair value	19,800,000	20,700,000
Institutional Counterparties | Interest Rate Swap Agreements
Assets:
Gross Amounts of Recognized Assets	121,000	155,000
Gross Amounts Offset in the Statements of Condition	0	0
Net Amounts of Assets Presented in the Statements of Condition	121,000	155,000
Derivative Asset, Netting Adjustments per Master Netting Arrangements	121,000	155,000
Gross Amounts Not Offset in the Statements of Condition - FV of collateral pledged	0	0
Derivative Assets, Net Amount	0	0
Liabilities:
Gross Amounts of Recognized Liabilities	19,883,000	20,853,000
Gross Amounts Offset in the Statements of Condition	0	0
Net Amounts of Liabilities Presented in the Statements of Condition	19,883,000	20,853,000
Derivative Liability, Netting Adjustments per Master Netting Arrangements	121,000	155,000
Derivative, Collateral, Right to Reclaim Securities	2,194,000	2,288,000
Derivative Liabilities, Net Amount	17,568,000	18,410,000
Private Institutions
Liabilities:
Repurchase Agreements, Gross Amounts of Recognized Liabilities	600,000,000	600,000,000
Repurchase Agreements, Gross Amounts Offset in the Statements of Condition	0	0
Repurchase Agreements, Net Amounts of Liabilities Presented in the Statements of Condition	600,000,000	600,000,000
Repurchase Agreements,Collateral, Right to Reclaim Securities	600,000,000	600,000,000
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral	0	0
Fair value of securities pledged	700,000,000	700,000,000
Government Entities
Liabilities:
Repurchase Agreements, Gross Amounts of Recognized Liabilities	197,213,000	170,049,000
Repurchase Agreements, Gross Amounts Offset in the Statements of Condition	0	0
Repurchase Agreements, Net Amounts of Liabilities Presented in the Statements of Condition	197,213,000	170,049,000
Repurchase Agreements,Collateral, Right to Reclaim Securities	197,213,000	170,049,000
Securities Sold under Agreements to Repurchase, Amount Offset Against Collateral	0	0
Fair value of investment securities pledged, not separately reported	$ 2,000,000,000	$ 1,800,000,000