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Shareholders' Equity (Narrative) (Details)
3 Months Ended
Mar. 31, 2017
USD ($)
vote
stock_class
$ / shares
shares
Mar. 31, 2016
$ / shares
Dec. 31, 2016
vote
$ / shares
shares
Sep. 06, 2011
USD ($)
Share Repurchases [Line Items]        
Number of classes of common stock | stock_class 3      
Preferred stock, authorized shares | shares 500,000.0   500,000.0  
Preferred stock, par value (in dollars per share) | $ / shares $ 0.01   $ 0.01  
Preferred stock, issued shares | shares 0   0  
Dividends declared per share (in dollars per share) | $ / shares $ 0.30 $ 0.30    
Common Class A [Member]        
Share Repurchases [Line Items]        
Number of votes | vote 1   1  
Share repurchase program, authorized amount | $       $ 100,000,000
Number of shares repurchased | shares 0      
Remaining authorized repurchases | $ $ 82,900,000      
Common Class B [Member]        
Share Repurchases [Line Items]        
Number of votes | vote 10   10  
Common Class C [Member]        
Share Repurchases [Line Items]        
Number of votes | vote 10   10