Offsetting (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Offsetting Assets [Line Items]
Gross amounts of recognized, asset	$ 23,797	[1]	$ 44,508	[1]
Gross amount offset in the balance sheet	0		0
Net amounts of asset/ liabilities presented in the balance sheet, asset	23,797		44,508
Gross amounts not offset in the balance sheet, financial instruments, asset	(5)		(2)
Gross amounts not offset in the balance sheet, cash collateral received/ pledged	0		0
Net amount, asset	23,792		44,506
Gross amounts of recognized, liability	(14,301)	[1]	(14,010)	[1]
Gross amount offset in the balance sheet	0		0
Net amounts presented in the balance sheet, liability	(14,301)		(14,010)
Gross amounts not offset in the balance sheet, financial instruments, liability	5		2
Gross amounts not offset in the balance sheet, cash collateral received	1,806		4,341
Net amount, liability	$ (12,490)		$ (9,667)

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