Annual report pursuant to Section 13 and 15(d)

Share-Based Awards and Cash-Based Awards - Additional Information (Details)

v3.8.0.1
Share-Based Awards and Cash-Based Awards - Additional Information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Share based compensation performance awards grant performance period 10 years    
Annual incentive awards payment period 90 days    
Common stock available for award under plans 13,363,792    
Recognized incentive compensation expense $ 8,065,000 $ 11,013,000 $ 10,242,000
Restricted Stock Units (RSUs)      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Shares granted, grant date fair value 5,900,000 9,300,000 9,400,000
Shares vested, vested date fair value 5,500,000 2,400,000 2,100,000
Unrecognized share-based compensation expense $ 6,200,000    
Recognition period for unrecognized compensation expense 2019-11    
Recognized incentive compensation expense $ 7,785,000 10,640,000 9,978,000
Restricted Shares      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Shares granted, grant date fair value 300,000 300,000 300,000
Shares vested, vested date fair value 100,000 100,000 100,000
Unrecognized share-based compensation expense $ 400,000    
Recognition period for unrecognized compensation expense 2020-04    
Recognized incentive compensation expense $ 280,000 373,000 358,000
2017 Cash-based Awards | Minimum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Adjusted EBITDA less interest expense $ 200,000,000    
2017 Annual Incentive Award Agreement      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Cash based award expected payment period 2018-03    
2016 Cash-based Awards      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Recognized incentive compensation expense $ 0 $ 0  
Cash based compensation payment period after achievement of financial condition   30 days  
2016 Cash-based Awards | Minimum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Adjusted EBITDA less interest expense   $ 300,000,000  
2015 Cash-based Awards      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Recognized incentive compensation expense     $ 0
Adjusted EBITDA and Adjusted EBITDA Margin      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Restricted stock units earning per share, minimum 0.00% 0.00% 0.00%
Restricted stock units earning per share, maximum 100.00% 100.00% 100.00%
Amended and Restated Incentive Compensation Plan      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Amendment increased the number of shares available in the Plan 7,700,000    
Directors Compensation Plan Share-Based Awards | Restricted Shares      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Vesting rights description Vesting occurs upon completion of the specified vesting period and one-third of each grant vests each year over a three-year period.    
Grant vesting period 3 years 3 years 3 years
Directors Compensation Plan      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Common stock available for award under plans 170,524