The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit that is attributable to changes in the income tax laws or rates.

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This element represents the amount of interest expense accrued as of the date of the statement of financial position for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity.

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- Definition

This element represents interest expense recognized for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity.

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Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
Income Taxes - Additional Information (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Income Tax [Line Items]
Change in effective tax rate due to acquisition of Credo	2.00%
Tax benefits not recognized for book purposes	$ 5,831,000	$ 5,831,000	$ 6,019,000
Recognized interest accrued related to unrecognized tax benefits	152,000	41,000	133,000
Accrued interest	420,000	269,000	229,000
Unrecognized tax benefits	5,831,000
Federal and State [Member]
Schedule Of Income Tax [Line Items]
Operating loss carry forwards	31,000,000
Domestic Tax Authority [Member]
Schedule Of Income Tax [Line Items]
Expiration date of operating loss carry forwards	2030 through 2032
State and Local Jurisdiction [Member]
Schedule Of Income Tax [Line Items]
Expiration date of operating loss carry forwards	2013 through 2032
Credo [Member]
Schedule Of Income Tax [Line Items]
Oil and natural gas percentage depletion carryforwards	$ 8,800,000