Revenue from Contracts with Customers (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) contract		Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2018 USD ($)
Segment Reporting Information [Line Items]
Retained earnings	$ 752,840		$ 799,402		$ 798,128
Gas gathering and processing revenues	223,730		207,176	$ 185,870
Adjustments due to ASC606 [Member]
Segment Reporting Information [Line Items]
Gas gathering and processing revenues	$ 4,970
Minimum
Segment Reporting Information [Line Items]
Contact duration	6 months
Number of days for drilling of one well	10 days
Maximum
Segment Reporting Information [Line Items]
Contact duration	3 years
Number of days for drilling of one well	90 days
Oil and Natural Gas
Segment Reporting Information [Line Items]
Revenue Satisfied at Point in Time, Transfer of Control	Revenues from sales we make are recognized when our customer obtains control of the sold product. For sales to other mid-stream and downstream oil and gas companies, this would occur at a point in time, typically on delivery to the customer.
Gas gathering and processing revenues	$ 0	[1]	0	0
Oil and Natural Gas | Adjustments due to ASC606 [Member]
Segment Reporting Information [Line Items]
Retained earnings					0
Drilling
Segment Reporting Information [Line Items]
Revenue Satisfied over Time, Method Used	At inception, the total transaction price will be estimated to include any applicable fixed consideration, unconstrained variable consideration (estimated day rate mobilization and demobilization revenue, estimated operating day rate revenue to be earned over the contract term, expected bonuses (if material and can be reasonably estimated without significant reversal), and penalties (if material and can be reasonably estimated without significant reversal)). Allocation rules under this new standard allow us to recognize revenues associated with our drilling contacts in materially the same manner as under the previous revenue accounting standard. A contract liability will be recorded for consideration received before the corresponding transfer of services. Those liabilities will generally only arise in relation to upfront mobilization fees paid in advance and are allocated/recognized over the entire performance obligation. Such balances will be amortized over the recognition period based on the same method of measure used for revenue.
Number of daywork contracts | contract	32
Revenue, Practical Expedient, Initial Application and Transition, Qualitative Assessment	The majority of our drilling contracts have an original term of less than one year; however, the remaining performance obligations under the contracts that have a longer duration are not material.
Gas gathering and processing revenues	$ 0	[1]	0	0
Drilling | Adjustments due to ASC606 [Member]
Segment Reporting Information [Line Items]
Retained earnings					0
Drilling | Long-term Contract with Customer [Member]
Segment Reporting Information [Line Items]
Number of daywork contracts | contract	24
Drilling | Minimum
Segment Reporting Information [Line Items]
Contact duration	6 months
Number of days for drilling of one well	10 days
Drilling | Minimum | Long-term Contract with Customer [Member]
Segment Reporting Information [Line Items]
Contact duration	2 months
Drilling | Maximum
Segment Reporting Information [Line Items]
Contact duration	3 years
Number of days for drilling of one well	90 days
Mid-Stream
Segment Reporting Information [Line Items]
Revenue Satisfied over Time, Method Used	Contract terms range from a single month to terms spanning a decade or more, some include evergreen provisions. Fees for mid-stream services (gathering, transportation, processing) are performance obligations and meet the criteria of over time recognition which could be considered a series of distinct performance obligations that represents one overall performance obligation of gas gathering and processing services.
Revenue, Practical Expedient, Initial Application and Transition, Qualitative Assessment	As stated previously, the contract term for mid-stream services is typically longer than one year. However, based on the guidance at 606-10-32-40, we determined some of the variable payment in mid-stream service agreements specifically relates to the entity’s efforts to satisfy the performance obligation and that “allocating the variable amount entirely to the distinct good or service is consistent with the allocation objective in paragraph 606-10-32-28.” Therefore, the practical expedient relates to this variable consideration: the commodity fee and the gathering fee.
Gas gathering and processing revenues	$ 312,417	[1]	$ 277,049	$ 237,785
Mid-Stream | Adjustments due to ASC606 [Member]
Segment Reporting Information [Line Items]
Retained earnings	$ 2,478				(1,274)
Adjustment to opening retained earnings, before tax					(1,700)
Adjustment to opening retained earnings, after tax					$ (1,300)
Mid-Stream | Minimum
Segment Reporting Information [Line Items]
Contact duration	5 years
Remaining term of contract	1 year
Mid-Stream | Maximum
Segment Reporting Information [Line Items]
Contact duration	10 years
Remaining term of contract	15 years

[1] The revenues for oil and natural gas occur at a point in time. The revenues for contract drilling and gas gathering and processing occur over time.