Fair Value Measurements (Details) (Recurring, USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Assets:
Total	$ 428,865	$ 542,974
Liabilities:
Derivative liabilities	67,939	141,639
Derivative liabilities, Valuation Technique	Income	Income
Cash and cash equivalents
Assets:
Cash and cash equivalents	291,062	295,522
Restricted cash and cash equivalents, Valuation Technique	Market	Market
Restricted cash and cash equivalents
Assets:
Cash and cash equivalents	137,803	247,452
Restricted cash and cash equivalents, Valuation Technique	Market	Market
Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets:
Total	428,865	542,974
Liabilities:
Derivative liabilities	0	0
Quoted Prices In Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Assets:
Cash and cash equivalents	291,062	295,522
Quoted Prices In Active Markets for Identical Assets (Level 1) | Restricted cash and cash equivalents
Assets:
Cash and cash equivalents	137,803	247,452
Significant Other Observable Inputs (Level 2)
Assets:
Total	0	0
Liabilities:
Derivative liabilities	67,939	85,410
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Assets:
Cash and cash equivalents	0	0
Significant Other Observable Inputs (Level 2) | Restricted cash and cash equivalents
Assets:
Cash and cash equivalents	0	0
Significant Unobservable Inputs (Level 3)
Assets:
Total	0	0
Liabilities:
Derivative liabilities	0	56,229
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Assets:
Cash and cash equivalents	0	0
Significant Unobservable Inputs (Level 3) | Restricted cash and cash equivalents
Assets:
Cash and cash equivalents	$ 0	$ 0