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Employee Benefit Plans - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2009
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]        
Accrued severance funds liability $ 3.2 $ 3.1    
Defined Contribution Pension Plan 401k        
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]        
Employer matching contribution as percentage of employee's salary deferral contributions       50.00%
Employer matching contribution as percentage of employee's eligible compensation       6.00%
Employer contributions amount $ 4.3 $ 3.4 $ 2.7