Resale and Repurchase Agreements (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Resale and Repurchase Agreements
Fair value of financial instruments received as collateral permitted to deliver or repledge	$ 100,000,000	$ 1,500,000,000
U.S. Government and federal agency obligations
Details on the composition of the outstanding repurchase agreements
Fair Value of Collateral Received that has been Repledged	103,562,000	1,478,081,000
Overnight | U.S. Government and federal agency obligations
Details on the composition of the outstanding repurchase agreements
Fair Value of Collateral Received that has been Repledged		1,204,641,000
Less than 30 days | U.S. Government and federal agency obligations
Details on the composition of the outstanding repurchase agreements
Fair Value of Collateral Received that has been Repledged	100,000,000
On Demand | U.S. Government and federal agency obligations
Details on the composition of the outstanding repurchase agreements
Fair Value of Collateral Received that has been Repledged	$ 3,562,000	$ 273,440,000