Balance Sheet Offsetting (Details) (Interest rate related instruments [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Interest rate related instruments [Member]
Offsetting of Derivative Assets
Gross amounts recognized	$ 2,694	$ 66
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	2,694	66
Financial instruments	(2,690)	(66)
Collateral	0	0
Net amount	4	0
Offsetting of Derivative Liabilities
Gross amounts recognized	47,897	73,067
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	47,897	73,067
Financial instruments	(2,690)	(66)
Collateral	(41,241)	(67,331)
Net amount	$ 3,966	$ 5,670