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Schedule II - Condensed Financial Information of Registrant - Condensed Balance Sheets (Parenthetical) (Detail) - $ / shares
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Condensed Financial Information Of Parent Company Only Disclosure [Abstract]        
Cumulative convertible preferred stock, par value $ 0.01 $ 0.01    
Cumulative convertible preferred stock, shares authorized 1,000,000 1,000,000    
Cumulative convertible preferred stock, shares issued 10,000 10,000    
Cumulative convertible preferred stock, shares outstanding 10,000 10,000    
Cumulative convertible preferred stock, minimum liquidation preference $ 9.99 $ 9.99    
Common stock, par value $ 0.01 $ 0.01    
Common stock, shares authorized 55,000,000 55,000,000    
Common stock, shares issued 45,778,000 45,324,000 45,525,000 44,769,000
Common stock, shares outstanding 34,735,000 35,052,000 35,110,000 35,102,000
Treasury stock, shares 11,043,000 10,272,000 10,415,000 9,667,000