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Preferred Shares - Additional Information (Detail) - $ / shares
Dec. 31, 2018
Dec. 31, 2017
May 18, 2016
Accelerated Share Repurchases [Line Items]      
Preferred stock, shares authorized 5,000,000 5,000,000  
Preferred stock, par value $ 0.01 $ 0.01  
Preferred stock, shares issued 0    
Series A Junior Participating Preferred Stock [Member]      
Accelerated Share Repurchases [Line Items]      
Preferred stock, shares authorized 400,000    
Preferred stock, par value     $ 0.01