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Defined Contribution Plans and Deferred Compensation - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]      
Expenses incurred for contribution plans $ 1,100,000 $ 1,100,000 $ 1,000,000.0
Deferred compensation payments 100,000 200,000 100,000
Amount of deferred compensation payable $ 1,300,000 1,400,000  
U.S. [Member]      
Defined Contribution Plan Disclosure [Line Items]      
Employee contribution limit per calendar year (as a percent of compensation) 80.00%    
Employer match of employee contributions of first level of eligible compensation (as a percent) 100.00%    
Percentage of eligible compensation, matched by employer, level one 2.00%    
Employer match of employee contributions of second level of eligible compensation (as a percent) 50.00%    
Percentage of eligible compensation matched by employer, level two 4.00%    
Expenses incurred for contribution plans $ 2,300,000 $ 2,000,000.0 $ 1,900,000
Italy [Member]      
Defined Contribution Plan Disclosure [Line Items]      
Annual deferred compensation provision for leaving indemnity, as a percentage of total commissions earned 3.50%    
Italy [Member] | Labor Force Concentration Risk [Member] | National Collective Labor Agreement [Member]      
Defined Contribution Plan Disclosure [Line Items]      
Number of employees, percentage 19.60%