Fair Value Measurements (Details 1) (Fair Value Recurring, USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets:
Derivative assets	$ 10,641	$ 10,945
Money market funds	10,720	5,997
Other derivative assets	1,353	1,419
Total	22,714	18,361
Liabilities:
Derivative liabilities	(19,148)	8,682
Total	(19,148)	8,682
Level 1
Assets:
Derivative assets	0	0
Money market funds	10,720	5,997
Other derivative assets	0	0
Total	10,720	5,997
Liabilities:
Derivative liabilities	0	0
Total	0	0
Level 2
Assets:
Derivative assets	10,641	10,945
Money market funds	0	0
Other derivative assets	0	0
Total	10,641	10,945
Liabilities:
Derivative liabilities	(19,148)	8,682
Total	(19,148)	8,682
Level 3
Assets:
Derivative assets	0	0
Money market funds	0	0
Other derivative assets	1,353	1,419
Total	1,353	1,419
Liabilities:
Derivative liabilities	0	0
Total	$ 0	$ 0