Acquisitions (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) drilling_location producing_well	Dec. 31, 2014 USD ($)	Mar. 31, 2015 customer
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement	Jan. 31, 2016
Vermillion [Member]
Business Acquisition [Line Items]
Producing wells | producing_well	75
Number of future drilling locations | drilling_location	112
Business Acquisition, Effective Date of Acquisition	Dec. 31, 2015
Business Combination, Consideration Transferred [Abstract]
Net cash paid	$ 16.0
Eagle Mountain [Member]
Business Acquisition [Line Items]
Customers acquired in acquisition | customer			6,500
Business Acquisition, Effective Date of Acquisition	Mar. 31, 2015
Business Combination, Consideration Transferred [Abstract]
Net cash paid	$ 11.4
Canyon Creek [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition	Dec. 17, 2014
Business Acquisition, Description of Acquired Entity	an additional interest in natural gas-producing properties in existing Wexpro-operated assets in the Canyon Creek Unit of southwestern Wyoming's Vermillion Basin
Business Combination, Consideration Transferred [Abstract]
Net cash paid	$ 52.6
Trail [Member]
Business Acquisition [Line Items]
Business Acquisition, Effective Date of Acquisition		Sep. 04, 2013
Business Acquisition, Date of Acquisition Agreement		Jul. 25, 2013
Business Combination, Consideration Transferred [Abstract]
Net cash paid		$ 104.3