Supplemental Oil and Gas Disclosures (Unaudited), Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
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
Number of years of experience of Evaluator	36 years
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	$ 2,988,464		$ 2,244,846		$ 1,784,920
Future production costs	(921,977)		(754,722)		(642,706)
Future development costs	(557,782)		(467,206)		(328,554)
Future income tax expense	(373,095)		(244,394)		(149,625)
Future net cash flows	1,135,610		778,524		664,035
Discount	(623,053)		(437,539)		(385,890)
Standardized Measure of discounted future net cash relating to proved reserves	512,557		340,985		278,145
Analysis of the changes in Standardized Measure [Roll Forward]
Standardized Measure, beginning of year	340,985		278,145		269,082
Sales and transfers of oil and gas produced, net of production costs	96,364		60,403		37,080
Net change in prices and development and production costs from prior year	150,504		169,969		60,710
Extensions, discoveries, and improved recovery, less related costs	147,275		156,456		73,236
Sales of minerals in place	(15,042)		(125,533)		(20,089)
Purchased of minerals in place	0		0		131
Revisions of previous quantity estimates	74,390		2,930		3,355
Change in timing and other	(82,653)		(62,861)		(88,309)
Change in future income tax expense	(40,636)		(45,532)		(9,799)
Accretion of discount	34,098		27,814		26,908
Standardized Measure, end of year	$ 512,557		$ 340,985		$ 278,145
Oil and gas prices considered in standardized measure of discounted future net cash flows [Abstract]
Oil (in dollars per Bbl)	95.28	[1]	97.33	[1]	95.14	[1]
Gas (in dollars per MMbtu)	4.35	[2]	3.67	[2]	2.86	[2]
Oil (in dollars per Bbl)	87.11	[3]	95.90	[3]	88.26	[3]
Gas (in dollars per MMBtu)	5.15	[4]	3.65	[4]	2.61	[4]
NGL's (in dollars per Bbl)	37.91	[5]	31.98	[5]	36.76	[5]

[1] The quoted oil price for the year ended December 31 of each year, 2012, 2013 and 2014 is the 12-month average first-day-of-the-month West Texas Intermediate spot price for each month of 2012, 2013 and 2014.

[2] The quoted gas price for the year ended December 31, 2012, 2013 and 2014 is the 12-month average first-day-of-the-month Henry Hub spot price for each month of 2012, 2013 and 2014.

[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.