Offsetting Assets and Liabilities (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Offsetting Assets and Liabilities [Abstract]
Derivative Asset, Fair Value, Gross Asset	$ 1,790,000	$ 2,148,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	1,790,000	2,148,000
Derivative Asset, Fair Value	1,790,000	2,148,000
Securities Sold Under Agreements to Repurchase, Gross	531,066,000	586,867,000
Securities Sold Under Agreements to Repurchase, Total	531,066,000	586,867,000
Securities Sold Under Agreements to Repurchase, Collateral, Right to Reclaim Securities	531,066,000	586,867,000
Securities Sold Under Agreements to Repurchase, Amount Offset Against Collateral, Total	0	0
Derivative Liability, Fair Value, Gross Liability	1,827,000	2,144,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	1,827,000	2,144,000
Derivative, Collateral, Right to Reclaim Cash	1,827,000	2,144,000
Derivative, Net Liability Position, Aggregate Fair Value	0	0
Offsetting Liabilities, Gross	532,893,000	589,011,000
Offsetting Liabilities, Total	532,893,000	589,011,000
Offsetting Liabilities, Securities Collateral	531,066,000	586,867,000
Offsetting Liabilities, Cash Collateral	1,827,000	2,144,000
Offsetting Liabilities, Net	$ 0	$ 0