Share-Based and Cash-Based Incentive Compensation (Tables)
   | 
12 Months Ended | 
Dec. 31, 2015  | 
| Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] | 
 
 | 
| Schedule of Restricted Stock Activity | 
A summary of activity related to Restricted Shares is as follows: 
 
  
| 
   
 | 
 2015 
 | 
   
 | 
   
 | 
 2014 
 | 
   
 | 
   
 | 
 2013 
 | 
   
 | 
 
| 
   
 | 
 Restricted Shares 
 | 
   
 | 
   
 | 
 Weighted Average Grant Date Fair Value Per Share 
 | 
   
 | 
   
 | 
 Restricted Shares 
 | 
   
 | 
   
 | 
 Weighted Average Grant Date Fair Value Per Share 
 | 
   
 | 
   
 | 
 Restricted Shares 
 | 
   
 | 
   
 | 
 Weighted Average Grant Date Fair Value Per Share 
 | 
   
 | 
 
| 
 Nonvested, beginning of period 
 | 
   
 | 
 43,210 
 | 
   
 | 
   
 | 
 $ 
 | 
 16.20 
 | 
   
 | 
   
 | 
   
 | 
 43,840 
 | 
   
 | 
   
 | 
 $ 
 | 
 15.96 
 | 
   
 | 
   
 | 
   
 | 
 43,687 
 | 
   
 | 
   
 | 
 $ 
 | 
 18.69 
 | 
   
 | 
 
| 
 Granted 
 | 
   
 | 
 56,540 
 | 
   
 | 
   
 | 
   
 | 
 6.19 
 | 
   
 | 
   
 | 
   
 | 
 18,815 
 | 
   
 | 
   
 | 
   
 | 
 18.60 
 | 
   
 | 
   
 | 
   
 | 
 27,450 
 | 
   
 | 
   
 | 
   
 | 
 12.75 
 | 
   
 | 
 
| 
 Vested 
 | 
   
 | 
 (21,520 
 | 
 ) 
 | 
   
 | 
   
 | 
 16.26 
 | 
   
 | 
   
 | 
   
 | 
 (19,445 
 | 
 ) 
 | 
   
 | 
   
 | 
 18.00 
 | 
   
 | 
   
 | 
   
 | 
 (27,297 
 | 
 ) 
 | 
   
 | 
   
 | 
 17.09 
 | 
   
 | 
 
| 
 Nonvested, end of period 
 | 
   
 | 
 78,230 
 | 
   
 | 
   
 | 
 $ 
 | 
 8.95 
 | 
   
 | 
   
 | 
   
 | 
 43,210 
 | 
   
 | 
   
 | 
 $ 
 | 
 16.20 
 | 
   
 | 
   
 | 
   
 | 
 43,840 
 | 
   
 | 
   
 | 
 $ 
 | 
 15.96 
 | 
   
 | 
 
 
 
  
 
 | 
| Schedule of Restricted Stock Awards Outstanding | 
Subject to the satisfaction of service conditions, the Restricted Shares outstanding as of December 31, 2015 are expected to vest as follows:  
  
| 
   
 | 
 Restricted Shares 
 | 
   
 | 
 
| 
 2016 
 | 
   
 | 
 34,265 
 | 
   
 | 
 
| 
 2017 
 | 
   
 | 
 25,115 
 | 
   
 | 
 
| 
 2018 
 | 
   
 | 
 18,850 
 | 
   
 | 
 
| 
 Total 
 | 
   
 | 
 78,230 
 | 
   
 | 
 
 
 
  
 
 | 
| Summary of Share Activity Related to Restricted Stock Units | 
A summary of activity related to RSUs is as follows:  
  
| 
   
 | 
 2015 
 | 
   
 | 
   
 | 
 2014 
 | 
   
 | 
   
 | 
 2013 
 | 
   
 | 
 
| 
   
 | 
 Restricted Stock Units 
 | 
   
 | 
   
 | 
 Weighted Average Grant Date Fair Value Per Share 
 | 
   
 | 
   
 | 
 Restricted Stock Units 
 | 
   
 | 
   
 | 
 Weighted Average Grant Date Fair Value Per Share 
 | 
   
 | 
   
 | 
 Restricted Stock Units 
 | 
   
 | 
   
 | 
 Weighted Average Grant Date Fair Value Per Share 
 | 
   
 | 
 
| 
 Nonvested, beginning of period 
 | 
   
 | 
 1,977,335 
 | 
   
 | 
   
 | 
 $ 
 | 
 15.29 
 | 
   
 | 
   
 | 
   
 | 
 1,331,753 
 | 
   
 | 
   
 | 
 $ 
 | 
 14.96 
 | 
   
 | 
   
 | 
   
 | 
 969,820 
 | 
   
 | 
   
 | 
 $ 
 | 
 22.70 
 | 
   
 | 
 
| 
 Granted 
 | 
   
 | 
 2,626,930 
 | 
   
 | 
   
 | 
   
 | 
 3.59 
 | 
   
 | 
   
 | 
   
 | 
 1,195,388 
 | 
   
 | 
   
 | 
   
 | 
 16.84 
 | 
   
 | 
   
 | 
   
 | 
 969,919 
 | 
   
 | 
   
 | 
   
 | 
 13.23 
 | 
   
 | 
 
| 
 Vested 
 | 
   
 | 
 (721,038 
 | 
 ) 
 | 
   
 | 
   
 | 
 13.23 
 | 
   
 | 
   
 | 
   
 | 
 (354,692 
 | 
 ) 
 | 
   
 | 
   
 | 
 18.59 
 | 
   
 | 
   
 | 
   
 | 
 (468,925 
 | 
 ) 
 | 
   
 | 
   
 | 
 26.93 
 | 
   
 | 
 
| 
 Forfeited 
 | 
   
 | 
 (409,148 
 | 
 ) 
 | 
   
 | 
   
 | 
 10.63 
 | 
   
 | 
   
 | 
   
 | 
 (195,114 
 | 
 ) 
 | 
   
 | 
   
 | 
 16.53 
 | 
   
 | 
   
 | 
   
 | 
 (139,061 
 | 
 ) 
 | 
   
 | 
   
 | 
 16.50 
 | 
   
 | 
 
| 
 Nonvested, end of period 
 | 
   
 | 
 3,474,079 
 | 
   
 | 
   
 | 
 $ 
 | 
 7.42 
 | 
   
 | 
   
 | 
   
 | 
 1,977,335 
 | 
   
 | 
   
 | 
 $ 
 | 
 15.29 
 | 
   
 | 
   
 | 
   
 | 
 1,331,753 
 | 
   
 | 
   
 | 
 $ 
 | 
 14.96 
 | 
   
 | 
 
 
 
  
 
 | 
| Schedule of Restricted Stock Units Outstanding | 
Subject to the satisfaction of service conditions, the RSUs outstanding as of December 31, 2015 are eligible to vest in the year indicated in the table below:  
  
| 
   
 | 
 Restricted Stock Units 
 | 
   
 | 
 
| 
 2016 
 | 
   
 | 
 1,003,604 
 | 
   
 | 
 
| 
 2017 
 | 
   
 | 
 2,470,475 
 | 
   
 | 
 
| 
 Total 
 | 
   
 | 
 3,474,079 
 | 
   
 | 
 
 
 
  
 
 | 
| Summary of Compensation Expense under Share-Based Payment Arrangements and Related Tax Benefit | 
A summary of compensation expense under share-based payment arrangements and the related tax benefit is as follows (in thousands):  
| 
   
 | 
 Year Ended December 31, 
 | 
   
 | 
 
| 
   
 | 
 2015 
 | 
   
 | 
   
 | 
 2014 
 | 
   
 | 
   
 | 
 2013 
 | 
   
 | 
 
| 
 Share-based compensation expense from: 
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
 
| 
 Restricted stock 
 | 
 $ 
 | 
 358 
 | 
   
 | 
   
 | 
 $ 
 | 
 369 
 | 
   
 | 
   
 | 
 $ 
 | 
 397 
 | 
   
 | 
 
| 
 Restricted stock units 
 | 
   
 | 
 9,978 
 | 
   
 | 
   
 | 
   
 | 
 13,150 
 | 
   
 | 
   
 | 
   
 | 
 11,128 
 | 
   
 | 
 
| 
 Common shares 
 | 
   
 | 
 (94 
 | 
 ) 
 | 
   
 | 
   
 | 
 1,225 
 | 
   
 | 
   
 | 
   
 | 
 — 
 | 
   
 | 
 
| 
 Total 
 | 
 $ 
 | 
 10,242 
 | 
   
 | 
   
 | 
 $ 
 | 
 14,744 
 | 
   
 | 
   
 | 
 $ 
 | 
 11,525 
 | 
   
 | 
 
| 
 Share-based compensation tax benefit: 
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
 
| 
 Tax benefit computed at the statutory rate 
 | 
 $ 
 | 
 3,585 
 | 
   
 | 
   
 | 
 $ 
 | 
 5,160 
 | 
   
 | 
   
 | 
 $ 
 | 
 4,034 
 | 
   
 | 
 
 
 
  
 
 | 
| Summary of Incentive Compensation Expense | 
A summary of incentive compensation expense is as follows (in thousands):  
| 
    
 | 
 Year Ended December 31, 
 | 
   
 | 
 
| 
   
 | 
 2015 
 | 
   
 | 
   
 | 
 2014 
 | 
   
 | 
   
 | 
 2013 
 | 
   
 | 
 
| 
 Share-based compensation included in: 
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
 
| 
 General and administrative 
 | 
 $ 
 | 
 10,242 
 | 
   
 | 
   
 | 
 $ 
 | 
 14,744 
 | 
   
 | 
   
 | 
 $ 
 | 
 11,525 
 | 
   
 | 
 
| 
 Cash-based incentive compensation included in: 
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
   
 | 
 
| 
 Lease operating expense 
 | 
   
 | 
 364 
 | 
   
 | 
   
 | 
   
 | 
 3,285 
 | 
   
 | 
   
 | 
   
 | 
 3,482 
 | 
   
 | 
 
| 
 General and administrative (1) 
 | 
   
 | 
 (233 
 | 
 ) 
 | 
   
 | 
   
 | 
 6,950 
 | 
   
 | 
   
 | 
   
 | 
 8,817 
 | 
   
 | 
 
| 
 Total charged to operating income 
 | 
 $ 
 | 
 10,373 
 | 
   
 | 
   
 | 
 $ 
 | 
 24,979 
 | 
   
 | 
   
 | 
 $ 
 | 
 23,824 
 | 
   
 | 
 
 
 
| 
   
 | 
 (1) 
 | 
 Adjustments to true up estimates to actual payments resulted in net credit balances to expense for 2015. 
 | 
   
 | 
 
 
 
 
 |