Intangible Assets (Details) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) a	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Finite-Lived Intangible Assets [Line Items]
Beginning balance	$ 172,166	$ 185,766	$ 185,766
Disposals			(32)
Amortization	(6,730)	$ 6,800	(13,568)
Ending balance	$ 165,436		$ 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	$ 165,400