Related Parties - Metalmark Capital and Monarch Natural Gas, LLC (Details) - director		6 Months Ended
	May 07, 2013	Jun. 30, 2017
Monarch Natural Gas, LLC | Investee | Metalmark
Related Party Transactions
Metalmark Capital's ownership percentage in Monarch (as a percent)	81.00%
Metalmark | Beneficial owner
Related Party Transactions
Number of directors who are managing directors of the related party		2
Minimum | Metalmark | Beneficial owner
Related Party Transactions
Beneficial ownership interest (as a percent)		5.00%