Debt (Details) (USD $)	1 Months Ended	6 Months Ended
	Apr. 30, 2011	Jun. 30, 2011	Apr. 13, 2011	Dec. 31, 2010
Debt obligations
Short-term Bank Loans and Notes Payable		$ 12,700,000		$ 5,300,000
Total outstanding debt		395,000,000		170,000,000
Total outstanding under Line of Credit and Credit Agreement		408,000,000
Short Term Line of Credit
Debt obligations
Line of credit, current borrowing capacity		40,000,000
Line of credit, maximum number of days which borrowings may be outstanding (in days)		30
Short-term Bank Loans and Notes Payable				5,300,000
Reference rate for interest rate		LIBOR plus
Line of credit, margin rate over LIBOR (as a percent)		1.40%
Weighted average interest rate on outstanding borrowings (as a percent)		1.60%		1.70%
Senior secured revolving credit facility (Credit Agreement - long term)
Debt obligations
Reference rate for interest rate	LIBOR	LIBOR
Revolving credit facility maximum borrowing base before amendment			875,000,000
Revolving credit facility maximum borrowing base after amendment			1,400,000,000
Lender commitments			875,000,000
Annual commitment fee on the unused portion of the credit agreement low end of range (as a percent)	0.35%	0.35%
Annual commitment fee on the unused portion of the credit agreement high end of range (as a percent)	0.50%	0.50%
Total outstanding debt		395,000,000		170,000,000
Letters of credit that have been issued under the facility		23,000,000
Remaining borrowing capacity available under the agreement		$ 444,000,000
Debt instrument covenant consolidated interest coverage ratio numerator		2.75
Debt instrument covenant consolidated interest coverage ratio denominator		1.0
Debt instrument covenant consolidated minimum current ratio numerator		1.0
Debt instrument covenant consolidated minimum current ratio denominator		1.0
Senior secured revolving credit facility (Credit Agreement - long term) | LIBOR
Debt obligations
Debt instrument basis spread on variable rate low end of range (as a percent)		1.50%	1.50%
Debt Instrument basis spread on variable Rate high end of range (as a percent)		2.50%	2.50%
Senior secured revolving credit facility (Credit Agreement - long term) | Prime
Debt obligations
Debt instrument basis spread on variable rate low end of range (as a percent)		0.50%	0.50%
Debt Instrument basis spread on variable Rate high end of range (as a percent)		1.50%	1.50%
10.25% Senior notes due 2014
Debt obligations
Interest rate on debt instrument (as a percent)		10.25%		10.25%
8.25% Senior subordinated notes due 2016.
Debt obligations
Interest rate on debt instrument (as a percent)		8.25%		8.25%