Revenue Recognition (ASC 606) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gathering and transportation lease revenues	$ 13,168		$ 25,486
Total revenues	17,039	$ 25,029	35,575	$ 50,836
Gathering and transportation
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contracts with customers	1,661	14,176	3,349	25,387
Midstream
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gathering and transportation lease revenues	13,168		25,486
Total revenues	14,829	14,176	28,835	25,387
Midstream | Accounting Standards Update 2014-09 | Balances without Adoption Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total revenues	14,829		28,835
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	13,168		25,486
Midstream | Gathering and transportation
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue from contracts with customers	1,661	$ 14,176	3,349	$ 25,387
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	14,829		28,835
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	$ (13,168)		$ (25,486)