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Stock-based Compensation - Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
Feb. 28, 2017
Sep. 30, 2017
Mar. 31, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
May 31, 2017
Dec. 31, 2016
Feb. 07, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Stock-based compensation capitalized   $ 0   $ 0 $ 0 $ 0      
Fair value assumptions, forfeiture rate         7.00% 7.00%      
Number of stock option exercised (in shares)   10,700   1,200 29,500 16,480      
Number of options outstanding forfeited (in shares)   0   0 0 0      
Income tax benefits from stock-based activity   $ 380,000   $ 10,000 $ 4,000,000 $ 52,000      
Excess tax benefits related to vested and exercised share-based compensation awards     $ 3,300,000            
Increase in basic earnings per share (in USD per share)     $ 0.38            
Class A Common Stock                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Number of stock option exercised (in shares)   89,800     1,000,000        
Restricted shares                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Restricted shares granted   0   28,000 855,000 54,000      
Weighted average fair value, grants in period (in USD per share)       $ 5.69 $ 21.94 $ 6.22      
Aggregate intrinsic value, grants in period       $ 157,600 $ 18,800,000 $ 337,600      
SARs                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Restricted shares granted   100,000   104,000 185,000 703,000      
Weighted average fair value, grants in period (in USD per share)   $ 16.51   $ 2.47 $ 14.30 $ 3.13      
Number of stock option exercised (in shares) 1,000,000 110,500   0 1,400,000 0      
Number of options outstanding forfeited (in shares)   0   2,250 17,500 24,250      
Long Term Incentive Plan                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Stock-based incentive plan expiration period         10 years        
Common stock reserved for issuance (in shares)   5,250,000     5,250,000   2,000,000 2,000,000 1,250,000
Stock Based Incentive Plans                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Cash outflow from stock based incentive plans   $ 263,000   $ 36,000 $ 448,000 $ 75,000