Revenue from Contracts with Customers (Revenue, Remaining Performance Obligation) (Details) - Mid-Stream [Member] $ in Thousands	Jun. 30, 2019 USD ($)
Minimum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Term of Contract	3 years
Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Term of Contract	9 years
Demand fee contracts [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Impact to Revenue	$ (4,565)
Demand fee contracts [Member] | July - December 2019
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Impact to Revenue	1,295
Demand fee contracts [Member] | 2020
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Impact to Revenue	(3,775)
Demand fee contracts [Member] | 2021
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Impact to Revenue	(3,501)
Demand fee contracts [Member] | 2022
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Impact to Revenue	1,380
Demand fee contracts [Member] | 2023 and Beyond
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining Impact to Revenue	$ 36