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The Incentive Stock Plans - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended
Feb. 28, 2017
Dec. 31, 2018
Dec. 31, 2017
Jan. 31, 2011
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Options granted   0 0  
Total intrinsic value of options exercised   $ 1,300,000 $ 1,900,000  
Fair value of options vested   $ 0 $ 1,300,000  
Incentive Stock Plan 2011 [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Common stock, shares authorized       2,200,456
Additional common shares authorized 1,000,000      
Expiration of Plan 2011   2021-01    
Contractual term of plan 2011   10 years    
Incentive Stock Plan 2011 [Member] | Subject To Award [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Common stock, shares authorized   3,000,000    
Incentive Stock Plan 2011 [Member] | Maximum [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Common stock, shares authorized 3,200,456      
Incentive Stock Plan 2007 [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Number of Common stock shares available   200,456