Impact of ASC 606 Adoption - Schedule of Impact of Adoption on Consolidated Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenues:
Total operating revenues	$ 190,138	$ 212,657	$ 415,511	$ 433,616
Expenses:
Production taxes	18,883	21,754	42,153	43,887
Gathering fees	24,181	20,642	47,238	41,571
Net income	(20,555)	499,037	26,933	409,338	$ 177,140
Natural Gas Sales
Revenues:
Total operating revenues	141,255	179,997	322,716	368,848
Oil Sales
Revenues:
Total operating revenues	43,167	30,732	84,451	62,081
Other Revenues
Revenues:
Total operating revenues	$ 5,716	$ 1,928	8,344	$ 2,687
Accounting Standards Update 2014-09 | Increase/ (Decrease)
Revenues:
Total operating revenues			415,674
Expenses:
Production taxes			42,169
Gathering fees			47,257
Net income			27,061
Accounting Standards Update 2014-09 | Increase/ (Decrease)
Revenues:
Total operating revenues			(163)
Expenses:
Production taxes			(16)
Gathering fees			(19)
Net income			(128)
Accounting Standards Update 2014-09 | Natural Gas Sales | Increase/ (Decrease)
Revenues:
Total operating revenues			322,879
Accounting Standards Update 2014-09 | Natural Gas Sales | Increase/ (Decrease)
Revenues:
Total operating revenues			(163)
Accounting Standards Update 2014-09 | Oil Sales | Increase/ (Decrease)
Revenues:
Total operating revenues			84,451
Accounting Standards Update 2014-09 | Other Revenues | Increase/ (Decrease)
Revenues:
Total operating revenues			$ 8,344