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Shares Repurchased - Additional Information (Detail) - USD ($)
12 Months Ended
Apr. 27, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Oct. 29, 2014
Class of Stock [Line Items]          
Repurchased common stock, value   $ 7,891,000 $ 39,379,000 $ 24,116,000  
Three-Year Share Repurchase Program [Member]          
Class of Stock [Line Items]          
Common stock purchase authorized amount         $ 100,000,000
Share repurchase program, increase in authorized amount $ 60,000,000        
Share repurchase program, extended term date Apr. 27, 2019        
Repurchased common stock, shares   697,664 3,778,932 1,190,356  
Repurchased common stock, value   $ 7,891,000 $ 39,379,000 $ 24,116,000  
Dollar amount remaining available for future share repurchases   $ 88,614,000