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Maximum Number Of Common Stock Vest As Percentage Of Performance Shares Granted

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Number of Performance Cash Units Granted

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One Percent Vest For Each One Percent Growth

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Percentage Of Grant That Will Vest For Metrics Met At Target Level

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Percentage Of Grant That Will Vest For Performance Met At Threshold Level

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Maximum percentage of performance based awards allowed to vest within a year.

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Percent of Performance Based Shares Vested

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Performance goals percentage weight for change in proved natural gas and oil reserves per debt adjusted share

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Performance goals percentage change in discretionary cash flow per debt adjusted share relative to defined peer groups percentage

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The total fair value of Performance-based equity awards for which the grantee gained the right during the reporting period, by satisfying performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Aggregate carrying value as of the balance sheet date of the liabilities for deferred compensation arrangements payable within one year (or the normal operating cycle, if longer). Represents currently earned compensation under cash arrangements (such as a profit-sharing plan, rabbi trust, and employee contract--excluding equity-based arrangements) that is not actually paid until a later date.

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Aggregate carrying value as of the balance sheet date of the liabilities for deferred compensation arrangements payable after one year (or the normal operating cycle, if longer). Represents currently earned compensation under cash arrangements (such as a profit-sharing plan, rabbi trust, and employee contract--excluding equity-based arrangements) that is not actually paid until a later date.

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Unrecognized cost of unvested share-based compensation awards.

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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.

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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).

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The number of employees affected by the modification of an equity-based compensation plan.

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Number of share options (or share units) exercised during the current period.

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Equity Incentive Compensation Plans and Other Employee Benefits - Additional Information (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) integer unit $ / shares age shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 unit	Dec. 31, 2014 shares	Dec. 31, 2013 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise of common stock options	0	0	0
Shares Vested From Special Retention Grant Of Performance-Based Shares			15,495
Unrecognized compensation cost \| $	$ 8,100
Weighted-average period (years)	1 year 9 months
Non-cash stock based compensation \| $	$ 7,226	$ 8,289	$ 11,941
Minimum age for employees to be eligible under employee directed savings plan \| age	21
Percentage of employee's contribution matched by the company	100.00%
Percentage of employee's pretax income	6.00%
Cash and common stock contributions \| $	$ 1,200	$ 1,000	$ 1,000
Percentage of employee's cash compensation reached under cash matching contributions	6.00%
2012 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	6,500,000
Number of shares available for grant	4,565,902
2016 Performance Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Plan Modification, Number of Employees Affected \| integer	23
Share-based Compensation Arrangement by Share-based Payment Award, Plan Modification, Incremental Compensation Cost \| $	$ 0
Adjustments to Additional Paid in Capital, Other \| $	$ 1,800
Percentage Of Original Award Converted To Nonvested Common Stock Award	89.00%
Number Of Units Converted To Nonvested Common Stock \| integer	592,472
Number Of Shares, Converted From Performance Cash Units	527,299
Number Of Units Not Converted To Nonvested Common Stock \| integer	65,173
2015 Performance Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Weighted percentage of stockholders return related to performance goals	60.00%
Performance goals percentage for change in discretionary cash flows	40.00%
Vested, Shares	286,652
Percent of Performance Based Shares Vested	104.10%
Maximum Number Of Cash Units Vest As Percentage Of Performance Cash Units Granted	200.00%
Number Of Performance Cash Units Granted \| unit				422,345
2015 Performance Program [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance-based awards allowed to vest within a year	25.00%
2015 Performance Program [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of total grant that will vest for metrics met at stretch level	200.00%
Percentage of total grant that will vest for metrics met at target level	100.00%
Percentage of performance-based awards allowed to vest within a year	50.00%
2014 Performance Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted percentage of stockholders return related to performance goals	60.00%
Performance goals percentage for change in discretionary cash flows	40.00%
Vested, Shares		166,023
Percent of Performance Based Shares Vested		106.70%
2014 Performance Program [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of total grant that will vest for metrics met at stretch level	200.00%
Percentage of total grant that will vest for metrics met at target level	100.00%
Percentage of performance-based awards allowed to vest within a year	25.00%
Two Thousand Eighteen Performance Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash Program Vesting Period	3 years
Closing Share Price, December 29, 2017 \| $ / shares	$ 5.13
Payout If Share Price Less Than $5.13 \| unit	0
One Percent Vest For Each One Percent Growth	1.00%
Payout If Relative TSR Is Less Than Median \| unit	0
Two Thousand And Seventeen Performance Program [Domain]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Plan Modification, Number of Employees Affected \| integer	34
Share-based Compensation Arrangement by Share-based Payment Award, Plan Modification, Incremental Compensation Cost \| $	$ 500
Adjustments to Additional Paid in Capital, Other \| $	$ 900
Percentage Of Original Award Converted To Nonvested Common Stock Award	100.00%
Number Of Units Converted To Nonvested Common Stock \| integer	619,006
Number Of Shares, Converted From Performance Cash Units	619,006
2013 Performance Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of total grant that will vest for metrics met at stretch level	200.00%
Weighted percentage of stockholders return related to performance goals	33.30%
Performance goals percentage for change in discretionary cash flows	33.30%
Performance goals percentage weight for change in proved properties	33.30%
Percentage of performance-based awards allowed to vest within a year	50.00%
Percentage of total grant that will vest for metrics met at target level	100.00%
Performance shares set as side at the end of plan						450,544
Percentage of performance-based awards allowed to vest within a year	25.00%
Maximum number of common stock vest as percentage of performance shares granted	200.00%
Vested, Shares			141,080
Percent of Performance Based Shares Vested			59.60%
2013 Performance Program [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of total grant that will vest for metrics met at stretch level	200.00%
Percentage of total grant that will vest for metrics met at target level	100.00%
Nonvested Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Fair value of performance-based shares vested in year \| $	$ (3,700)	$ (2,900)	$ (1,700)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	1,185,809	791,129	686,500
Non-cash stock based compensation \| $	$ 6,036	$ 5,852	$ 6,696
Vested, Shares	694,505	513,376	451,329
Nonvested Equity Common Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	1 year
Non-cash stock based compensation \| $	$ 1,138	$ 690	$ 883
Cash-Based Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Nonvested Performance Cash Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent \| $	$ 300	3,000	$ 2,900
Deferred Compensation Cash-based Arrangements, Liability, Current \| $		$ 1,400
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	935,293	669,043	646,572
Vested, Shares	286,652	0	0
Fair Value Performance Based Cash Unit Awards Vested \| $	$ 1,500	$ 0
Nonvested Performance-Based Equity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of performance-based shares vested in year \| $	$ 0	$ (600)	$ (1,200)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	0	0	0
Non-cash stock based compensation \| $	$ 0	$ 558	$ 1,808
Vested, Shares	0	166,023	156,575
Nonvested Performance-Based Equity [Member] \| 2014 Performance Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period					315,661
Absolute Performance [Member] \| Two Thousand Eighteen Performance Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	150.00%
Relative TSR [Member] \| Two Thousand Eighteen Performance Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	50.00%
Absolute Performance and Relative TSR [Member] \| Two Thousand Eighteen Performance Program [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	200.00%
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of performance-based shares vested in year \| $	$ (1,100)	$ (200)	$ (700)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	226,244	193,878	98,974
Vested, Shares	187,566	68,486	97,299