Balance Sheet Offsetting (Details) (Interest rate related instruments [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Interest rate related instruments [Member]
Offsetting of Derivative Assets
Gross amounts of recognized assets	$ 63	$ 66
Gross amounts offset in the balance sheet	0	0
Net amounts of assets presented in the balance sheet	63	66
Financial instruments not offset in the balance sheet	(63)	(66)
Collateral not offset in the balance sheet	0	0
Net amount	0	0
Offsetting of Derivative Liabilities
Gross amounts of recognized liabilities	66,771	73,067
Gross amounts offset in the balance sheet	0	0
Net amounts of liabilities presented in the balance sheet	66,771	73,067
Financial instruments not offset in the balance sheet	(63)	(66)
Collateral not offset in the balance sheet	(59,536)	(67,331)
Net amount	$ 7,172	$ 5,670