Annual report pursuant to Section 13 and 15(d)

Capital Structure and Per Share Data - Additional Information (Details)

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Capital Structure and Per Share Data - Additional Information (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
Class
Vote
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Capital Structure And Per Share Data [Line Items]    
Preferred stock shares authorized 3,000,000  
Preferred stock, issued 0  
Number of classes of common stock | Class 2  
Class A convertible preferred stock    
Capital Structure And Per Share Data [Line Items]    
Preferred stock shares authorized 300,000  
Preferred Stock par value (in dollars per share) | $ / shares $ 0.10  
Preferred stock shares redeemed 13,801.5  
Preferred stock redemption price (in dollars per share) | $ / shares $ 1,000  
Series I Preferred Stock    
Capital Structure And Per Share Data [Line Items]    
Preferred stock authorized (in shares) 100,000  
Series II Preferred Stock    
Capital Structure And Per Share Data [Line Items]    
Preferred stock authorized (in shares) 100,000  
Series III Preferred Stock    
Capital Structure And Per Share Data [Line Items]    
Preferred stock authorized (in shares) 100,000  
Class A common stock    
Capital Structure And Per Share Data [Line Items]    
Common stock, shares authorized 100,000,000 100,000,000
Common stock, par value (in dollars per share) | $ / shares $ 0.01 $ 0.01
Common stock, number of votes per share | Vote 1  
Number of shares of class A common stock issuable against each share of class B common stock 1  
Authorized amount expend on repurchase of shares | $   $ 695,000,000.0
Common stock class A, shares repurchased 33,476,159 32,290,493
Common stock class A, share repurchase price per share (in dollars per share) | $ / shares $ 17.85  
Remaining authorized amount | $ $ 83,600,000  
Class B common stock    
Capital Structure And Per Share Data [Line Items]    
Common stock, shares authorized 30,000,000 30,000,000
Common stock, par value (in dollars per share) | $ / shares $ 0.01 $ 0.01
Common stock, number of votes per share | Vote 10