Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
Capital Structure and Per Share Data - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2017
USD ($)
Class
Vote
$ / shares
shares
Dec. 31, 2016
$ / shares
shares
Dec. 31, 2015
shares
Capital Structure And Per Share Data [Line Items]      
Preferred stock shares authorized 3,000,000    
Preferred stock, issued 0 0 0
Preferred stock, outstanding 0 0 0
Number of classes of common stock | Class 2    
Class A Convertible Preferred Stock [Member]      
Capital Structure And Per Share Data [Line Items]      
Preferred stock shares authorized 300,000    
Preferred Stock Par Value | $ / shares $ 0.10    
Preferred stock shares redeemed 13,801.5    
Preferred stock redemption price | $ / shares $ 1,000    
Series I Preferred Stock [Member]      
Capital Structure And Per Share Data [Line Items]      
Class A Convertible Preferred Stock Shares Authorized 100,000    
Series II Preferred Stock [Member]      
Capital Structure And Per Share Data [Line Items]      
Class A Convertible Preferred Stock Shares Authorized 100,000    
Series III Preferred Stock [Member]      
Capital Structure And Per Share Data [Line Items]      
Class A Convertible Preferred Stock Shares Authorized 100,000    
Common Class A [Member]      
Capital Structure And Per Share Data [Line Items]      
Common stock, shares authorized 100,000,000 100,000,000  
Common stock, par value | $ / 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    
Common stock class A, shares repurchased 32,290,493 30,263,196  
Common stock class A, share repurchase price per share | $ / shares $ 17.76    
Remaining authorized amount | $ $ 107,700,000    
Antidilutive stock options excluded in computation of diluted earnings per share   200,000 400,000
Common Class B [Member]      
Capital Structure And Per Share Data [Line Items]      
Common stock, shares authorized 30,000,000 30,000,000  
Common stock, par value | $ / shares $ 0.01 $ 0.01  
Common stock, number of votes per share | Vote 10