Resale and Repurchase Agreements (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Resale and Repurchase Agreements
Fair value of financial instruments held as collateral that the entity was permitted to deliver or repledge	$ 137,900,000	$ 1,500,000,000
Details on the composition of the outstanding repurchase agreements
Fair value of collateral held that has been repledged	137,900,000	1,500,000,000
Carrying value of securities sold under agreements to repurchase	159,386,000	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 held that has been repledged	106,991,000	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 held that has been repledged	50,052,000
On Demand | U.S. Government and federal agency obligations
Details on the composition of the outstanding repurchase agreements
Fair value of collateral held that has been repledged	$ 2,343,000	$ 273,440,000