Revenue from Contracts with Customers (Revenue Impact of the Adoption of ASC606) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Adoption of ASC606 [Line Items]
Oil and natural gas revenues										$ 423,059		$ 357,744	$ 294,221
Oil and natural gas operating costs										131,675		130,789	120,184
Oil and natural gas gross profit	[1]	$ (108,068)	$ 49,216	$ 40,915	$ 38,833	$ 37,211	$ 27,181	$ 24,462	$ 32,657
Gas gathering and processing revenues										223,730		207,176	185,870
Deferred tax benefit										(10,865)		(57,683)	(71,209)
Net income (loss)										(39,767)		117,848	(135,624)
Adjustments due to ASC606 [Member]
Adoption of ASC606 [Line Items]
Oil and natural gas revenues										(17,518)
Oil and natural gas operating costs										(17,518)
Gas gathering and processing revenues										4,970
Deferred tax benefit										1,218
Net income (loss)										3,752
Amounts without the adoption of ASC606 [Member]
Adoption of ASC606 [Line Items]
Oil and natural gas revenues										440,577
Oil and natural gas operating costs										149,193
Gas gathering and processing revenues										218,760
Deferred tax benefit										(12,083)
Net income (loss)										(43,519)
Oil and Natural Gas
Adoption of ASC606 [Line Items]
Oil and natural gas revenues										423,059	[2]	357,744	294,221
Oil and natural gas operating costs										136,870		135,532	126,739
Oil and natural gas gross profit										291,384
Gas gathering and processing revenues										0	[2]	$ 0	$ 0
Oil and Natural Gas | Adjustments due to ASC606 [Member]
Adoption of ASC606 [Line Items]
Oil and natural gas gross profit										0
Oil and Natural Gas | Amounts without the adoption of ASC606 [Member]
Adoption of ASC606 [Line Items]
Oil and natural gas gross profit										$ 291,384

[1] Gross income (loss) excludes general and administrative expense, interest expense, (gain) loss on disposition of assets, gain (loss) on derivatives, income taxes, and other income (loss).

[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.