Derivatives (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Derivatives
Derivative assets, fair value	$ 203,000	$ 26,000
Linked Transactions, at fair value	12,704,000	55,801,000
Swaps liabilities, at fair value	(63,034,000)	(114,220,000)
Swaps | Hedging | Assets.
Derivatives
Derivative assets, fair value	203,000	26,000
Notional amount of derivative assets	100,000,000
Swaps | Hedging | Liabilities.
Derivatives
Swaps liabilities, at fair value	(63,034,000)	(114,220,000)
Notional amount of derivative liabilities	2,420,000,000
Linked Transactions
Derivatives
Associated accrued interest receivable	185,000	1,100,000
Associated accrued interest payable	38,000	412,000
Linked Transactions | Non-Hedging | Assets.
Derivatives
Linked Transactions, at fair value	$ 12,704,000	$ 55,801,000