Supplemental Oil and Gas Disclosures (Unaudited), Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves (Details) Boe in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2017 USD ($) Boe $ / bbl $ / MMBTU	Dec. 31, 2016 USD ($) Boe $ / bbl $ / MMBTU	Dec. 31, 2015 USD ($) Boe $ / bbl $ / MMBTU	Dec. 31, 2017 USD ($) Boe	Dec. 31, 2016 USD ($) Boe	Dec. 31, 2015 USD ($) Boe
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Period for standardize measure of discounted future net cash flows		12 months
Discount rate (in hundredths)		10.00%
Future net cash inflows after income taxes discounted at 10% annual discount rate to arrive at Standardized Measure [Abstract]
Future cash inflows					$ 2,035,619	$ 999,716	$ 1,241,334
Future production costs					(609,921)	(357,917)	(438,784)
Future development costs					(461,619)	(267,836)	(338,316)
Future income tax expense					(83,915)	0	0
Future net cash flows					880,164	373,963	464,234
Discount					(474,423)	(213,363)	(266,983)
Standardized Measure of discounted future net cash relating to proved reserves		$ 160,600	$ 197,251	$ 512,557	$ 405,741	$ 160,600	$ 197,251
Analysis of the changes in Standardized Measure [Roll Forward]
Standardized Measure, beginning of year		160,600	197,251	512,557
Sales and transfers of oil and gas produced, net of production costs		63,764	32,834	37,249
Net change in prices and development and production costs from prior year		159,661	(58,425)	(488,160)
Extensions, discoveries, and improved recovery, less related costs		129,277	5,531	63,341
Sales of minerals in place		(8,583)	(4,433)	(197)
Purchases of minerals in place		1,238	0	0
Revisions of previous quantity estimates		31,044	12,317	(49,602)
Change in timing and other		1,908	21,468	20,419
Change in future income tax expense		(21,700)	0	124,886
Accretion of discount		16,060	19,725	51,256
Standardized Measure, end of year		$ 405,741	$ 160,600	$ 197,251
Oil and gas prices considered in standardized measure of discounted future net cash flows [Abstract]
Oil (in dollars per Bbl) | $ / bbl	[1]	51.34	42.74	50.12
Gas (in dollars per MMbtu) | $ / MMBTU	[2]	2.99	2.50	2.63
Oil (in dollars per Bbl) | $ / bbl	[3]	46.83	35.54	41.25
Gas (in dollars per MMBtu) | $ / MMBTU	[4]	1.79	1.41	2.36
NGL's (in dollars per Bbl) | $ / bbl	[5]	13.19	5.17	10.52
Oil Equivalents [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Sales of minerals in place | Boe		1,312	1,232	43
Proved Developed and Undeveloped Reserves, Production, Energy | Boe		2,698	2,262	2,181
Proved Undeveloped Reserve (Energy) | Boe					43,631	29,639	25,996
Proved Developed and Undeveloped Reserves, Production, Energy | Boe		4,747	3,424	(11,324)
Extensions and discoveries | Boe		19,768	1,537	14,332
Proved Developed Reserves | Boe					21,720	15,018	17,194

[1] The quoted oil price for the year ended December 31 of each year, 2015, 2016 and 2017 is the 12-month unweighted average first-day-of-the-month West Texas Intermediate spot price for each month of 2015, 2016 and 2017.

[2] The quoted gas price for the year ended December 31, 2015, 2016 and 2017 is the 12-month unweighted average first-day-of-the-month Henry Hub spot price for each month of 2015, 2016 and 2017.

[3] The oil price is the realized price at the wellhead as of December 31 of each year after the appropriate differentials have been applied.

[4] The gas price is the realized price at the wellhead as of December 31 of each year after the appropriate differentials have been applied.

[5] The NGL price is the realized price as of December 31 of each year after the appropriate differentials have been applied.