Intangible Assets (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($) a	Dec. 31, 2017 USD ($)
Finite-Lived Intangible Assets [Line Items]
Beginning balance	$ 172,166	$ 185,766
Disposals		(32)
Amortization	(3,365)	(13,568)
Ending balance	$ 168,801	$ 172,166
Customer Contracts
Finite-Lived Intangible Assets [Line Items]
Agreement term (in years)	15 years
Dedicated acreage | a	35,000
Useful life	15 years
Ending balance	$ 168,800