Debt Level 4 (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Debt Instrument [Line Items]
Loss on exchange of Senior Exchangeable Notes	$ (210,000)	$ 0	$ (839,000)	$ 0
Line of Credit Facility, Current Borrowing Capacity	300,000,000		300,000,000
Line of Credit Facility, Maximum Borrowing Capacity	350,000,000		350,000,000
Performance bonds under credit facility	14,500,000		14,500,000
Line of Credit Facility, Remaining Borrowing Capacity	285,500,000		285,500,000
Performance Bonds	17,900,000		17,900,000
Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.75%		1.75%
Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%		2.50%
Debt Conversion Requested 2 [Member] | Convertible Debt [Member]
Debt Instrument [Line Items]
NumberOfRequestsForConversionOfDebt		5
NumberOfDebtInstrumentsConverted			888
Convertible Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	300,000,000		300,000,000
Debt Instrument, Maturity Date			Oct. 31, 2011
Debt Instrument, Interest Rate, Stated Percentage	0.25%		0.25%
Debt Instrument, Interest Rate, Effective Percentage	7.48%		7.48%
Debt Instrument, Unamortized Discount	(2,183,000)		(2,183,000)		(8,864,000)
Long-term Debt, Gross	91,930,000		91,930,000		156,407,000
Amortization of Debt Discount (Premium)	1,800,000	3,900,000	4,000,000	7,700,000
FaceValueOfDebtPerInstrument			1,000
Debt Instrument, Convertible, Conversion Price	$ 45.51		$ 45.51
Debt Instrument, Convertible, Number of Equity Instruments			21.9738
PercentNotesTradingAboveFaceValue	243.00%		243.00%		197.00%
VarianceTradeValueToFaceValue	131,500,000		131,500,000		151,700,000
Number of Debt Instruments Outstanding	91,930		91,930		156,407
NumberOfRequestsForConversionOfDebt			9
NumberOfDebtInstrumentsConverted			17,909
Debt Conversion, Converted Instrument, Amount			17,900,000
Debt Conversion, Converted Instrument, Shares Issued			213,936
Loss on exchange of Senior Exchangeable Notes			200,000
Long-term Debt	$ 89,747,000		$ 89,747,000		$ 147,543,000