Summary of Significant Accounting Policies - Major Customers and Associated Percentage of Revenue (Detail) - Sales Revenue, Net [Member] - Customer Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue, Major Customer [Line Items]
Major customers and associated percentage of revenue	27.00%	63.00%	70.00%
Antero Resources Corporation [Member]
Revenue, Major Customer [Line Items]
Major customers and associated percentage of revenue		14.00%	19.00%
ARM Energy Management [Member]
Revenue, Major Customer [Line Items]
Major customers and associated percentage of revenue			11.00%
Concord Energy, LLC [Member]
Revenue, Major Customer [Line Items]
Major customers and associated percentage of revenue		12.00%
Emera Energy Services [Member]
Revenue, Major Customer [Line Items]
Major customers and associated percentage of revenue	17.00%
EnLink Midstream Operating [Member]
Revenue, Major Customer [Line Items]
Major customers and associated percentage of revenue		17.00%	21.00%
Marathon Petroleum [Member]
Revenue, Major Customer [Line Items]
Major customers and associated percentage of revenue	10.00%
Sequent Energy Management [Member]
Revenue, Major Customer [Line Items]
Major customers and associated percentage of revenue		20.00%	19.00%