Supplemental Oil and Gas Disclosures (Tables)

12 Months Ended

Dec. 31, 2017

Extractive Industries [Abstract]

Schedule of Capitalized Costs Related to Oil, Natural Gas and NGL Activities and Related Accumulated Depletion, Depreciation and Amortization

Aggregate amounts of capitalized costs relating to our oil, natural gas and NGL activities and the aggregate amount of related accumulated depletion, depreciation and amortization as of the dates indicated are presented below (in thousands):

	December 31,
	2017			2016
Proved properties	$	2,440,811		$	2,235,835
Unproved oil and gas properties, not subject to amortization		72,002			72,360
Total oil and gas properties		2,512,813			2,308,195
Less: Accumulated depletion and amortization		(1,423,829	)		(1,268,276	)
Net capitalized costs	$	1,088,984		$	1,039,919
Depletion and amortization rate per Boe	$	14.85		$	13.82

Schedule of Costs Incurred in Oil, Natural Gas and NGL Property Acquisition, Exploration and Development Activities

The following table reflects the costs incurred in oil, natural gas and NGL property acquisition, exploration and development activities during the years indicated (in thousands). Costs incurred also include new asset retirement obligations established in the current year, as well as increases or decreases to the asset retirement obligations resulting from changes to cost estimates during the year.

	Year Ended December 31,
	2017		2016		2015
Property acquisition costs:
Proved properties	$	1,108	$	77,906	$	68,463
Unproved properties, not subject to amortization		5,778		15,919		39,265
Total property acquisition costs		6,886		93,825		107,728
Exploration costs		82,887		27,807		25,908
Development costs		114,846		195,869		228,257
Total costs incurred	$	204,619	$	317,501	$	361,893

Schedule of Estimated Proved Reserves at Net Ownership Interest

The following table presents our estimated proved reserves at our net ownership interest:

	Oil (MBbls)			Gas (MMcf)			NGL (MBbls)			Oil Equivalent (MBoe)
Total proved reserves at December 31, 2014		46,120			136,232			4,096			72,921
Revision of previous estimates		(3,435	)		(22,580	)		207			(6,991	)
Production		(5,161	)		(21,458	)		(588	)		(9,325	)
Purchases of reserves		4,029			30,527			385			9,502
Extensions and discoveries		4,801			6,503			481			6,366
Total proved reserves at December 31, 2015		46,354			129,224			4,581			72,473
Revision of previous estimates		(1,712	)		10,024			(352	)		(394	)
Production		(5,126	)		(19,001	)		(603	)		(8,896	)
Purchases of reserves		11,128			11,208			950			13,946
Extensions and discoveries		21,722			19,149			1,660			26,573
Total proved reserves at December 31, 2016		72,366			150,604			6,236			103,702
Revision of previous estimates		(2,673	)		(15,860	)		250			(5,067	)
Production		(7,048	)		(16,308	)		(706	)		(10,472	)
Extensions and discoveries		10,159			9,220			767			12,462
Total proved reserves at December 31, 2017		72,804			127,656			6,547			100,625
Total proved developed reserves as of:
December 31, 2015		33,016			90,432			3,383			51,471
December 31, 2016		45,753			96,122			4,032			65,805
December 31, 2017		37,460			77,577			3,315			53,704
Total proved undeveloped reserves as of:
December 31, 2015		13,338			38,792			1,198			21,002
December 31, 2016		26,613			54,482			2,204			37,897
December 31, 2017		35,344			50,079			3,232			46,921

(1) One Boe is equal to six Mcf of natural gas or one Bbl of oil or NGLs based on an approximate energy equivalency. This is an energy content correlation and does not reflect a value or price relationship between the commodities.

Schedule of Standardized Measure of Discounted Future Net Cash Flows Related to Interest in Proved Oil, Natural Gas and NGL Reserves

The following table reflects the standardized measure of discounted future net cash flows relating to our interest in proved oil, natural gas and NGL reserves (in thousands):

	December 31,
	2017			2016			2015
Future cash inflows	$	4,308,863		$	3,390,612		$	2,786,828
Future costs:
Production		(815,509	)		(775,354	)		(1,363,585	)
Development and abandonment		(823,164	)		(664,254	)		(646,161	)
Future net cash flows before income taxes		2,670,190			1,951,004			777,082
Future income tax expense		—			—			—
Future net cash flows before income taxes		2,670,190			1,951,004			777,082
Discount at 10% annual rate		(862,521	)		(614,969	)		(174,101	)
Standardized measure of discounted future net cash flows	$	1,807,669		$	1,336,035		$	602,981

Schedule of Base Prices Used in Determining Standardized Measure

See the following table for base prices used in determining the standardized measure:

	Year Ended December 31,
	2017		2016		2015
Oil price per Bbl	$	51.36	$	40.02	$	50.72
Natural gas prices per Mcf	$	3.20	$	2.66	$	2.75
NGL price per Bbl	$	24.64	$	14.96	$	17.60

Schedule of Principal Changes in Standardized Measure of Discounted Future Net Cash Flows

Principal changes in the standardized measure of discounted future net cash flows attributable to our proved oil, natural gas and NGL reserves are as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
Standardized measure, beginning of year	$	1,336,035		$	602,981		$	1,888,958
Changes during the year:
Sales, net of production costs		(288,942	)		(114,625	)		(117,344	)
Net change in prices and production costs		555,100			80,174			(1,879,436	)
Changes in future development costs		(156,282	)		2,292			92,182
Development costs incurred		146,687			108,484			273,532
Accretion of discount		133,603			60,298			188,896
Net change in income taxes		—			—			—
Purchases of reserves		—			222,581			229,052
Extensions and discoveries		328,565			479,833			91,722
Sales of reserves		—			—			—
Net change due to revision in quantity estimates		(113,629	)		(5,685	)		(103,842	)
Changes in production rates (timing) and other		(133,468	)		(100,298	)		(60,739	)
Total		471,634			733,054			(1,285,977	)
Standardized measure, end of year	$	1,807,669		$	1,336,035		$	602,981