Supplementary Information on Oil and Gas Operations—Unaudited - Standardized Measure (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Future Net Cash Flows [Abstract]
Future cash flows	$ 1,711,404	$ 1,243,627	$ 728,878
Future production costs	(372,690)	(295,666)	(215,195)
Future development costs	(244,784)	(185,188)	(110,825)
Future income taxes	(121,192)	(37,404)	(9,642)
Future net cash flows	972,738	725,369	393,216
10% annual discount	(424,176)	(274,189)	(162,393)
Standardized measure of discounted future net cash flows	$ 548,562	$ 451,180	$ 230,823	$ 303,881

Name:	us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlowsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of estimated future accumulated cash inflow from the sale of proved oil and gas reserves.

+ References

+ Details

Name:	us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesCashInflows
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of estimated future accumulated cash outflow for costs to be incurred in developing proved oil and gas reserves.

+ References

+ Details

Name:	us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesDevelopmentCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of estimated future accumulated cash outflow for income tax, based on the future income less future expense derived from production and sale of proved oil and gas reserves.

+ References

+ Details

Name:	us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesIncomeTaxExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after future accumulated cash outflow for development and production costs and future income tax, of estimated future accumulated cash inflow from the sale of proved oil and gas reserves.

+ References

+ Details

Name:	us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesNetCashFlows
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of estimated future accumulated cash outflow for costs to be incurred in producing proved oil and gas reserves.

+ References

+ Details

Name:	us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesProductionCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of discount on future accumulated cash inflow, after deducting future accumulated cash outflow for development and production costs and future income tax, from sale of proved oil and gas reserves, using a discount rate of ten percent a year.

+ References

+ Details

Name:	us-gaap_FutureNetCashFlowsRelatingToProvedOilAndGasReservesTenPercentAnnualDiscountForEstimatedTimingOfCashFlows
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of discounted future accumulated cash inflow relating to proved oil and gas reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 30

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 35

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62500-109447

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 55

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=34713648&loc=d3e63123-109448

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 31

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447

+ Details

Name:	us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant