Offsetting (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Offsetting [Abstract]
Gross amounts of recognized, asset	[1]	$ 17,901	$ 21,521
Gross amount offset in the balance sheet		0	0
Net amounts of asset/ liabilities presented in the balance sheet, asset		17,901	21,521
Gross amounts not offset in the balance sheet, financial instruments, asset		(135)	(766)
Gross amounts not offset in the balance sheet, cash collateral received/ pledged		(9,200)	(8,536)
Net amount, asset		8,566	12,219
Gross amounts of recognized, liability	[1]	(34,862)	(27,977)
Gross amount offset in the balance sheet		0	0
Net amounts presented in the balance sheet, liability		(34,862)	(27,977)
Gross amounts not offset in the balance sheet, financial instruments, liability		135	766
Gross amounts not offset in the balance sheet, cash collateral received		43,499	14,858
Net amount, liability		$ 8,772	$ (12,353)

[1] Amounts include all derivative instruments, irrespective of whether there is a legally enforceable master netting arrangement in place.