Derivatives (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Derivatives
Derivative assets, fair value	$ 324,000	$ 203,000
Linked Transactions, at fair value	12,572,000	12,704,000
Swaps liabilities, at fair value	(50,839,000)	(63,034,000)
Swaps | Hedging | Assets.
Derivatives
Derivative assets, fair value	324,000	203,000
Notional amount of derivative assets	100,000,000
Swaps | Hedging | Liabilities.
Derivatives
Swaps liabilities, at fair value	(50,839,000)	(63,034,000)
Notional amount of derivative liabilities	2,414,000,000
Linked Transactions
Derivatives
Associated accrued interest receivable	175,000	185,000
Associated accrued interest payable	50,000	38,000
Linked Transactions | Non-Hedging | Assets.
Derivatives
Linked Transactions, at fair value	$ 12,572,000	$ 12,704,000