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Significant Accounting Policies - Additional Information (Detail)
$ in Thousands
12 Months Ended
Dec. 31, 2018
USD ($)
Segment
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Significant Accounting Policies [Line Items]        
Number of operating segment | Segment 1      
Cash, cash equivalents and restricted cash $ 178,444 $ 146,113 $ 153,894 $ 162,275
Restricted cash $ 3,625 $ 3,610    
Expected dividend rate 0.00%      
Description of Income tax benefit, likelihood of realized upon ultimate settlement The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement.      
Benefit related to remeasurement of deferred tax assets and liabilities as result of filing tax return $ 200      
Minimum [Member]        
Significant Accounting Policies [Line Items]        
Income tax examination, likelihood of settlement, percentage 50.00%      
ASC 606 [Member]        
Significant Accounting Policies [Line Items]        
Revenue, practical expedient, incremental costs of obtaining contract true      
Accounting Standards Update No. 2016-16 [Member]        
Significant Accounting Policies [Line Items]        
Cumulative-effect adjustment to retained earnings $ 400      
Lexington, MA [Member]        
Significant Accounting Policies [Line Items]        
Restricted cash 2,600      
Cambridge MA [Member]        
Significant Accounting Policies [Line Items]        
Restricted cash $ 1,000