Revenue Recognition (ASC 606) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gathering and transportation lease revenues	$ 12,318
Total revenues	18,536	$ 25,807
Gathering and transportation
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contracts with customers	1,688	11,211
Midstream
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gathering and transportation lease revenues	12,318
Total revenues	14,006
Midstream | Accounting Standards Update 2014-09 | Balances without Adoption Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total revenues	14,006
Midstream | Accounting Standards Update 2014-09 | Effect of change Higher/(Lower)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gathering and transportation lease revenues	12,318
Midstream | Gathering and transportation
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contracts with customers	1,688	$ 11,211
Midstream | Gathering and transportation | Accounting Standards Update 2014-09 | Balances without Adoption Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contracts with customers	14,006
Midstream | Gathering and transportation | Accounting Standards Update 2014-09 | Effect of change Higher/(Lower)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contracts with customers	$ (12,318)