Quarterly report pursuant to Section 13 or 15(d)

Summary of Incentive Compensation Expense (Detail)

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Summary of Incentive Compensation Expense (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]        
Share-based compensation charged to operating income $ 2,695 $ 3,159 $ 4,950 $ 5,818
Cash-based incentive compensation charged to operating income 2,771   7,694 3,778
Total incentive compensation charged to operating income 5,466 3,159 12,644 9,596
Lease Operating Expense
        
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]        
Cash-based incentive compensation charged to operating income 747   2,140 1,900
General and Administrative Expense
        
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]        
Cash-based incentive compensation charged to operating income $ 2,024   $ 5,554 $ 1,878