Capital Stock, Repurchases of Common Stock (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Jul. 31, 2018
Oct. 31, 2015
Aug. 31, 2013
Dec. 31, 1998
Repurchases of Common Stock [Abstract]              
Class A common stock repurchased $ 825 $ 69,565 $ 71,731        
1998 Stock Repurchase Plan [Member]              
Repurchases of Common Stock [Abstract]              
Authorized amount             $ 10,000
Increase in authorized amount           $ 400,000  
2015 Stock Repurchase Plan [Member]              
Repurchases of Common Stock [Abstract]              
Authorized amount         $ 500,000    
2018 Stock Repurchase Plan [Member]              
Repurchases of Common Stock [Abstract]              
Authorized amount       $ 500,000      
Amount available for repurchases 470,200            
Treasury Stock [Member]              
Repurchases of Common Stock [Abstract]              
Class A common stock repurchased $ 825 $ 69,565 $ 71,731        
Treasury Stock [Member] | 2015 Stock Repurchase Plan [Member]              
Repurchases of Common Stock [Abstract]              
Class A common stock repurchased (in shares)   500,000 1,200,000        
Class A common stock repurchased   $ 40,600 $ 71,700        
Treasury Stock [Member] | 2018 Stock Repurchase Plan [Member]              
Repurchases of Common Stock [Abstract]              
Class A common stock repurchased (in shares) 14,000 400,000          
Class A common stock repurchased $ 800 $ 29,000