Leases (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Adoption of ASC842 [Line Items]
Operating leases under ASC 840 future minimum payments due in next year			$ 4,600
Operating leases under ASC 840 future minimum payments due in two years			1,700
Operating leases under ASC 840 future minimum payments due in three years			400
Average working interest in operated properties	87.00%
Operating right of use asset	$ 4,551		$ 0
Total operating lease liability	4,321
Operating lease liability not yet commenced	$ 1,700
Number of compressors under finance lease agreement	20
Finance lease term	7 years
Finance Lease Obligations, Current	$ 4,000
Finance Lease Obligations, Noncurrent	$ 6,400
Discount rate finance leases	4.00%
Maintenance	$ 3,695
Interest	525
Finance leases, future minimum payments, average annual payment	$ 4,300
Finance lease fair market value percentage for purchase	10.00%
Accounting Standards Update 2016-02 [Member]
Adoption of ASC842 [Line Items]
Operating right of use asset		$ 3,700
Total operating lease liability		$ 3,500
Minimum [Member]
Adoption of ASC842 [Line Items]
Term of contract for operating lease liabilities not yet commenced	1 year
Maximum [Member]
Adoption of ASC842 [Line Items]
Term of contract for operating lease liabilities not yet commenced	3 years