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Stock-based Compensation - Narrative (Details) - USD ($)
1 Months Ended 3 Months Ended 6 Months Ended
May 31, 2017
Feb. 28, 2017
Jun. 30, 2017
Mar. 31, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 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 options outstanding forfeited (in shares)     0   0 0 0  
Number of stock option exercised (in shares)     10,800   1,600 18,800 15,300  
Income tax benefits from stock-based activity     $ 280,000   $ 28,000 $ 3,600,000 $ 42,000  
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)     150,000     934,100    
Restricted shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Weighted average fair value, grants in period (in USD per share)     $ 21.94   $ 6.77 $ 21.94 $ 6.77  
Aggregate intrinsic value, grants in period     $ 18,800,000   $ 180,000 $ 18,800,000 $ 180,000  
SARs                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Weighted average fair value, grants in period (in USD per share)     $ 11.70   $ 3.26 $ 11.70 $ 3.25  
Number of options outstanding forfeited (in shares)     17,500   12,000 17,500 22,000  
Number of stock option exercised (in shares)   1,000,000 212,700   0 1,300,000 0  
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   1,250,000
Increase in number of shares of common stock (in shares) 2,000,000              
Stock Based Incentive Plans                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Cash outflow from stock based incentive plans     $ 0   $ 14,000 $ 185,000 $ 39,000