Stock-based Compensation Plans - Additional Information 1 (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Market-based TSR
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 9,700,000	$ 9,100,000
Market-based TSR awards for 2014-2016 performance period
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Actual performance payout adjustment	89,000
Percentage of performance period grants adjusted for actual payout	40.00%
Performance Based Unit Production Growth Per Share And Reserve Growth Per Share
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 124,000