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Accounts Receivable and Revenues from Contracts with Customers - Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Gathering, processing and transportation	$ 4,928	$ 2,399	$ 12,861	$ 7,505
Net Income (Loss) Available to Common Stockholders, Basic	16,276	(5,947)	24,050	43,463
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Gathering, processing and transportation	5,482		14,431
Net Income (Loss) Available to Common Stockholders, Basic	16,276		24,050
Accounting Standards Update 2014-09 [Member] \| Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Gathering, processing and transportation	(554)		(1,570)
Net Income (Loss) Available to Common Stockholders, Basic	0		0
Oil and Gas, Exploration and Production [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	117,059	29,963	290,033	92,387
Oil and Gas, Exploration and Production [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	117,059		290,033
Oil and Gas, Exploration and Production [Member] \| Accounting Standards Update 2014-09 [Member] \| Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	0		0
Oil and Condensate [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	5,976	2,393	14,455	6,738
Oil and Condensate [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	6,530		16,025
Oil and Condensate [Member] \| Accounting Standards Update 2014-09 [Member] \| Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	(554)		(1,570)
Natural Gas, Production [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	3,768	$ 1,977	10,470	$ 6,200
Natural Gas, Production [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	3,768		10,470
Natural Gas, Production [Member] \| Accounting Standards Update 2014-09 [Member] \| Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	0		0
Oil and Gas, Refining and Marketing [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	143		388
Oil and Gas, Refining and Marketing [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	143		388
Oil and Gas, Refining and Marketing [Member] \| Accounting Standards Update 2014-09 [Member] \| Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 0		$ 0