Long-Term Debt Additional Information (Details) (USD $)			0 Months Ended		3 Months Ended	9 Months Ended	0 Months Ended			0 Months Ended			9 Months Ended	0 Months Ended			0 Months Ended				9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	May 15, 2016 3.25% Convertible Senior Notes due 2016	Nov. 15, 2010 3.25% Convertible Senior Notes due 2016	Sep. 30, 2014 3.25% Convertible Senior Notes due 2016 Rate	Sep. 30, 2014 3.25% Convertible Senior Notes due 2016 Rate	Oct. 15, 2022 7.75% Senior Notes due 2022	Oct. 03, 2012 7.75% Senior Notes due 2022	Sep. 30, 2014 7.75% Senior Notes due 2022 Rate	May 21, 2018 Revolving Credit Facility	May 21, 2013 Revolving Credit Facility	Nov. 05, 2010 Revolving Credit Facility	Sep. 30, 2014 Revolving Credit Facility	Apr. 30, 2010 PDCM Credit Facility	Sep. 30, 2014 PDCM Credit Facility Rate	Dec. 31, 2013 PDCM Credit Facility Rate	Jul. 02, 2013 PDCM Second Lien Term Loan	Sep. 30, 2014 PDCM Second Lien Term Loan Rate	Dec. 31, 2013 PDCM Second Lien Term Loan Rate	Sep. 30, 2014 RNG Credit Facility [Member]	Sep. 30, 2014 First Payment 3.25% Convertible Senior Notes due 2016	Sep. 30, 2014 First Payment 7.75% Senior Notes due 2022	Sep. 30, 2014 Second Payment 3.25% Convertible Senior Notes due 2016	Sep. 30, 2014 Second Payment 7.75% Senior Notes due 2022	Sep. 30, 2014 Revolving Credit Facility Rate	Dec. 31, 2013 Revolving Credit Facility	Sep. 30, 2014 Maximum Borrowing Base [Member] Revolving Credit Facility
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage					3.25%	3.25%			7.75%
Debt Instrument, Issuance Date				Nov. 15, 2010				Oct. 03, 2012									Jul. 02, 2013
Debt Instrument, Maturity Date			May 15, 2016				Oct. 15, 2022
Debt Instrument, Frequency of Periodic Payment																					May 15	April 15	November 15	October 15
Debt agreement Amendment date											May 21, 2013
3.25% Convertible Debt, Liability Component ($)				$ 94,300,000
Effective Interest Rate on Convertible Debt						7.40%
Debt Instrument, Convertible, Terms of Conversion Feature						Upon conversion, the Convertible Notes may be settled, at our election, in shares of our common stock, cash or a combination of cash and shares of our common stock. We have initially elected a net-settlement method to satisfy our conversion obligation, which allows us to settle the principal amount of the Convertible Notes in cash and to settle the excess conversion value in shares, as well as cash in lieu of fractional shares.
Convertible Note, If-converted Value in Excess of Principal					21,400,000
Line of Credit Facility, Initiation Date												Nov. 05, 2010		Apr. 30, 2010
Line of Credit Facility, Maximum Borrowing Capacity ($)													1,000,000,000
Line of Credit Facility, Current Borrowing Capacity ($)													450,000,000		105,000,000												700,000,000
Additional borrowing base available													250,000,000
Long-term Line of Credit																									68,000,000	0
Line of Credit Facility, Expiration Date										May 21, 2018
Debt Instrument, Covenant Description													The revolving credit facility contains covenants customary for agreements of this type, with the most restrictive being certain financial tests on a quarterly basis. The financial tests, as defined per the revolving credit facility, include requirements to: (a) maintain a minimum current ratio of 1.00 to 1.00 and (b) not exceed a maximum leverage ratio of 4.25 to 1.00.
PDC Irrevocable Standby Letter of Credit ($)																				11,700,000
Line of Credit Facility, Remaining Borrowing Capacity													370,300,000
Weighted Average Interest Rate															3.50%	3.70%		8.50%	8.50%						4.10%
Proportionate Share of PDCM Credit Facility ($)															53,000,000
PDCM second lien term loan	$ 15,000,000	$ 15,000,000																$ 30,000,000