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 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]        
Share-based compensation charged to operating income $ 3,507 $ 3,319 $ 8,457 $ 9,137
Cash-based incentive compensation charged to operating income 2,915 3,995 10,609 7,772
Total incentive compensation charged to operating income 6,422 7,314 19,066 16,909
Lease Operating Expense
        
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]        
Cash-based incentive compensation charged to operating income 724 947 2,864 2,846
General and Administrative Expense
        
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]        
Cash-based incentive compensation charged to operating income $ 2,191 $ 3,048 $ 7,745 $ 4,926