Commitments and Contingencies - Other Commitments (Details) $ in Thousands	1 Months Ended			3 Months Ended	12 Months Ended
	Jun. 30, 2014 USD ($)	May 31, 2014 USD ($)	Apr. 30, 2014 USD ($) mi	Sep. 30, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Pipeline connection agreement with Meadowlark
Other Commitment
Commitment amount	$ 55,000		$ 14,600		$ 25,000
Period under the agreement	7 years		5 years
Length of pipeline lateral which would be built, owned and operated | mi			4
Pipeline Connection Agreement With Tesoro High Plains [Member]
Other Commitment
Commitment amount		$ 36,400			9,900
Period under the agreement		7 years
Minimum quarterly commitment amount					1,500
Pipeline connection agreement with Tesoro Logistics
Other Commitment
Commitment amount					$ 0
Ownership interest					60.00%
Payment to accelerate and terminate agreement				$ 13,100
Natural Gas Transportation and Reservation Agreement [Member]
Other Commitment
Commitment amount					$ 6,100
Period under the agreement					5 years
Rail Spur And Dock Access Right Agreements [Member]
Other Commitment
Commitment amount					$ 27,100
Expense under agreements					$ 900	$ 900	$ 1,000