Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation and Cash-Based Incentive Compensation (Schedule of Incentive Compensation Expense) (Detail)

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Share-Based Compensation and Cash-Based Incentive Compensation (Schedule of Incentive Compensation Expense) (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Share-based compensation charged to operating income $ 3,159 $ 1,835 $ 5,818 $ 3,662
Cash-based incentive compensation charged to operating income   4,407 3,778 8,251
Total incentive compensation charged to operating income 3,159 6,242 9,596 11,913
Parent Company
        
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Share-based compensation charged to operating income 3,159 1,835 5,818 3,662
Lease operating expense
        
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Share-based compensation charged to operating income   116   233
Cash-based incentive compensation charged to operating income   1,119 1,900 2,199
General and administrative
        
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]        
Share-based compensation charged to operating income 3,159 1,719 5,818 3,429
Cash-based incentive compensation charged to operating income   $ 3,288 $ 1,878 $ 6,052