Long-Term Debt Additional Information (Details) - USD ($) $ in Thousands							3 Months Ended	9 Months Ended
	Oct. 15, 2022	May. 21, 2022	May. 15, 2016	Oct. 03, 2012	Nov. 15, 2010	Nov. 05, 2010	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
3.25% Convertible Senior Notes due 2016
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage							3.25%	3.25%
Debt Instrument, Issuance Date					Nov. 15, 2010
Debt Instrument, Maturity Date			May 15, 2016
3.25% Convertible Debt, Liability Component ($)					$ 94,300
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. Per the terms of the Convertible Notes, we have currently elected the 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							$ 28,800
7.75% Senior Notes due 2022
Debt Instrument
Debt Instrument, Interest Rate, Stated Percentage							7.75%	7.75%
Debt Instrument, Issuance Date				Oct. 03, 2012
Debt Instrument, Maturity Date	Oct. 15, 2022
Revolving Credit Facility
Debt Instrument
Debt agreement Amendment date							Sep. 30, 2015
Line of Credit Facility, Initiation Date						Nov. 05, 2010
Line of Credit Facility, Maximum Borrowing Capacity ($)							$ 1,000,000	$ 1,000,000
Line of Credit Facility, Current Borrowing Capacity ($)							450,000	$ 450,000
Line of Credit Facility, Expiration Date		May 21, 2020
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.
Line of Credit Facility, Remaining Borrowing Capacity							388,300	$ 388,300
RNG Credit Facility [Member]
Debt Instrument
PDC Irrevocable Standby Letter of Credit ($)							11,700	$ 11,700
First Payment | 3.25% Convertible Senior Notes due 2016
Debt Instrument
Debt Instrument, Frequency of Periodic Payment								May 15
First Payment | 7.75% Senior Notes due 2022
Debt Instrument
Debt Instrument, Frequency of Periodic Payment								April 15
Second Payment | 3.25% Convertible Senior Notes due 2016
Debt Instrument
Debt Instrument, Frequency of Periodic Payment								November 15
Second Payment | 7.75% Senior Notes due 2022
Debt Instrument
Debt Instrument, Frequency of Periodic Payment								October 15
Revolving Credit Facility
Debt Instrument
Long-term Line of Credit							$ 50,000	$ 50,000	$ 56,000
Weighted Average Interest Rate							2.70%	2.70%	4.10%
Maximum Borrowing Base [Member] | Revolving Credit Facility
Debt Instrument
Line of Credit Facility, Current Borrowing Capacity ($)							$ 700,000	$ 700,000