Commitments and Contingencies (Narrative) (Details) - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Long-term Purchase Commitment [Line Items]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 5,100,000
Operating Leases, Future Minimum Payments, Due in Two Years	2,100,000
Operating Leases, Future Minimum Payments, Due in Three Years	600,000
Operating Leases, Future Minimum Payments, Due in Four Years	100,000
Operating Leases, Rent Expense, Net	$ 7,200,000	$ 6,400,000
Number of compressors under capital lease agreement	20
Capital lease term	7 years
Capital Leases, Future Minimum Payments Due, Next Twelve Months	$ 6,195,000
Capital Leases, Future Minimum Payments Due in Two Years	6,195,000
Capital Leases, Future Minimum Payments Due in Three Years	5,322,000
Maintenance	4,601,000
Interest	756,000
Capital leases, future minimum payments, average annual payment	$ 4,200,000
Capital lease fair market value percentage for purchase	10.00%
Percentage of repurchase of limited units outstanding	20.00%
Repurchase Of Limited Units Outstanding Amount	$ 1,700	$ 2,900
Drilling Equipment [Member]
Long-term Purchase Commitment [Line Items]
Other Commitment, Due in Next Twelve Months	$ 10,064,000
Capital Addition Purchase Commitments [Member] | Oil and Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Description	as part of the Superior transaction, we entered into a contractual obligation that commits us to spend $150.0 million to drill wells in the Granite Wash/Buffalo Wallow area over three years starting January 1, 2019. This amount is already included in our drilling plan. For each dollar of the $150.0 million that we do not spend (over the three year period), we would forgo receiving $0.58 of future distributions from our 50% ownership interest in our consolidated mid-stream subsidiary. If we elected not to drill or spend any money in the designated area over the three year period, the maximum amount we could forgo from distributions would be $87.0 million.
Long-term Purchase Commitment, Amount	$ 150,000,000
Long-term Purchase Commitment, Period	3 years