Long-Term Debt (Details) (USD $)				1 Months Ended		3 Months Ended				3 Months Ended					0 Months Ended			0 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Holdings LLC	Mar. 31, 2013 Senior Revolving Credit Facility, due 2017 item	Oct. 31, 2012 Senior Revolving Credit Facility, due 2017	Mar. 31, 2013 Senior Revolving Credit Facility, due 2017	Feb. 28, 2013 Senior Revolving Credit Facility, due 2017	Dec. 31, 2012 Senior Revolving Credit Facility, due 2017	Mar. 31, 2012 Senior Revolving Credit Facility, due 2017	Mar. 31, 2013 Senior Revolving Credit Facility, due 2017 Minimum	Mar. 31, 2013 Senior Revolving Credit Facility, due 2017 Maximum item	Mar. 31, 2013 Senior Notes, due 2020	Dec. 31, 2012 Senior Notes, due 2020	Oct. 03, 2012 Senior Notes, due 2020	Oct. 02, 2012 Senior Notes, due 2020 Prior to October 2015	Oct. 02, 2012 Senior Notes, due 2020 Prior to October 2016	Oct. 02, 2012 Senior Notes, due 2020 Eagle Property Acquisition	Oct. 02, 2012 Senior Notes, due 2020 Maximum	Oct. 02, 2012 Senior Notes, due 2020 Maximum Prior to October 2015	Oct. 02, 2012 Credit Facility Eagle Property Acquisition
Long-Term Debt
Credit Facility - senior loan facility				$ 196,450,000		$ 196,450,000		$ 94,000,000				$ 600,000,000	$ 600,000,000	$ 600,000,000
Total long-term debt	796,450,000	694,000,000
Maximum borrowing capacity				500,000,000		500,000,000
Borrowing base				285,000,000		285,000,000	250,000,000
Interest rate, description						LIBOR
Interest rate added to base rate (as a percent)										1.75%	2.75%
Weighted-average interest rate (as a percent)				2.40%		2.40%			3.10%
Commitment fee, option one (as a percent)						0.375%
Commitment fee, option two (as a percent)						0.50%
Additional borrowing base redeterminations at company request per 6 month period following each scheduled borrowing base redetermination											1
Period during which Company may request additional redetermination of borrowing base				6 months
Percentage of outstanding loans and other obligations held by lenders, on whose behalf the administrative agent may request for redetermination of borrowing base										0.67
Number of equal successive monthly payments to make repayment on reduction of borrowing base				6
Period for commencement of repayment of equal successive monthly payments following the administrative agent's notice regarding borrowing base reduction				30 days
Debt to EBITDA ratio											4.0
Current ratio										1.0
Actual current ratio						1.40%
Actual Debt to EBITDA				3.48%		3.48%
Interest rate (as a percent)																	10.75%
Estimated proceeds from the offering (net of the initial purchasers' discount and related offering expenses)																				582,000,000
Repayment of outstanding facility balance					182,900,000
Ownership interest (as a percent)			100.00%
Percentage of debt that can be redeemed																			35.00%
Redemption price, expressed as percentage of principal amount												101.00%			110.75%
Redemption price, percentage																100.00%
Increase in interest rate of debt on nonfulfillment of condition (as a percent)																		1.00%
Estimated fair value of the Notes												$ 657,000,000
Effective annual interest rate (as a percent)												11.10%