Revenue from Contracts with Customer (Narrative) (Details) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018 USD ($)		Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) contract		Sep. 30, 2017 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Retained earnings	$ 830,680			$ 830,680			$ 798,128	$ 799,402
Gas gathering and processing revenues	57,823		$ 51,399	167,926		$ 150,493
Net income	21,123		3,705	37,138		28,693
Income from operations	40,191		18,027	$ 100,787		58,551
Drilling [Member]
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 Contracts, Daywork | contract				34
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	[2]	0
Oil and Natural Gas [Member]
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	[2]	0
Mid-Stream [Member]
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	82,882	[1]	$ 69,057	$ 232,938	[2]	$ 198,632
Minimum [Member] | Drilling [Member]
Segment Reporting Information [Line Items]
Contract Duration				6 months
Number of Days for Drilling of Wells				10 days
Minimum [Member] | Mid-Stream [Member]
Segment Reporting Information [Line Items]
Contract Duration				5 years
Remaining Term of Contract				4 years
Maximum [Member] | Drilling [Member]
Segment Reporting Information [Line Items]
Contract Duration				3 years
Number of Days for Drilling of Wells				90 days
Maximum [Member] | Mid-Stream [Member]
Segment Reporting Information [Line Items]
Contract Duration				10 years
Remaining Term of Contract				5 years
Short-term Contract with Customer [Member] | Drilling [Member]
Segment Reporting Information [Line Items]
Contract Duration				2 months
Long-term Contract with Customer [Member] | Drilling [Member]
Segment Reporting Information [Line Items]
Contract Duration				3 years
Number of Contracts, Daywork | contract				21
Adjustments due to ASC606 [Member]
Segment Reporting Information [Line Items]
Gas gathering and processing revenues	1,300			$ 3,671
Net income	982			2,772
Adjustments due to ASC606 [Member] | Drilling [Member]
Segment Reporting Information [Line Items]
Retained earnings							0
Adjustments due to ASC606 [Member] | Oil and Natural Gas [Member]
Segment Reporting Information [Line Items]
Retained earnings							0
Net income	0			0
Income from operations	0			0
Adjustments due to ASC606 [Member] | Mid-Stream [Member]
Segment Reporting Information [Line Items]
Retained earnings	$ 1,498			$ 1,498
Adjustment to opening retained earnings, before tax							(1,687)
Adjustment to opening retained earnings, after tax							$ (1,274)
Gathering service contracts [Member] | Minimum [Member] | Mid-Stream [Member]
Segment Reporting Information [Line Items]
Remaining Term of Contract				1 year
Gathering service contracts [Member] | Maximum [Member] | Mid-Stream [Member]
Segment Reporting Information [Line Items]
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.

[2] 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.