Stock- Based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Based Compensation Activity [Line Items]
Stock based compensation	$ 13,399	$ 8,914	$ 8,462
Stock based compensation capitalized into oil and gas properties	4,288	3,010	2,775
Exercise price of stock options outstanding, minimum	$ 6.97
Exercise price of stock options outstanding, maximum	$ 53.20
Restricted stocks issued, shares	670,818	597,062	395,869
Restricted stocks issued, value	21,085,000	14,100,000	6,251,000
Unrecognized compensation cost, weighted average period of recognition	1 year 9 months 18 days
Unrecognized compensation cost	18,547,000
Adjustments to additional paid-in capital related to net tax effect of stock options exercises and restricted stock vesting	814,000	735,000	(2,000)
Restricted Stock
Stock Based Compensation Activity [Line Items]
Stock based compensation	13,308	8,796	8,263
Restricted Stock \| Minimum
Stock Based Compensation Activity [Line Items]
Vesting period of stock options	1 year
Restricted Stock \| Maximum
Stock Based Compensation Activity [Line Items]
Vesting period of stock options	3 years
Stock Options
Stock Based Compensation Activity [Line Items]
Stock based compensation	$ 91	$ 118	$ 199
2009 plan \| All Employee
Stock Based Compensation Activity [Line Items]
Vesting period of stock options	5 years
Period after which stock option will expire subsequent to award	10
2009 plan \| Non - Employee Directors
Stock Based Compensation Activity [Line Items]
Vesting period of stock options	3 years
Period after which stock option will expire subsequent to award	10

Share based compensation arrangement by share based payment award award expiration period.

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- Definition

Stock based compensation capitalized into oil and gas properties.

+ References

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- Definition

Adjustment to additional paid in capital related to the net effect of excess tax benefits and tax deficiencies associated with an equity-based compensation plan other than an employee stock ownership plan (ESOP).

+ References

No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

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

-Publisher FASB

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Aggregate unrecognized cost of share-based awards, other than options, made to employees under an equity-based compensation plan, that have yet to vest.

+ References

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

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- Definition

Aggregate value of stock related to Restricted Stock Awards issued during the period.

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