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Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended
Sep. 30, 2018
Mar. 31, 2018
Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Allocation of recognized period costs, capitalized amount $ 224   $ 148
Employee Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares authorized for issuance under stock incentive plan (in shares) 1,800,000    
Shares available for future grant (in shares)   220,000  
Purchase price as a percentage of the lesser of the market value of such shares at either the beginning or the end of each nine-month offering period 85.00%    
Percentage of employee compensation that may be uses to purchase common stock through payroll deductions, maximum 10.00%    
Granted (in shares) 0    
2005 Stock Incentive Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares authorized for issuance under stock incentive plan (in shares) 15,252,000    
Exercise price of stock option, percentage 100.00%    
Shares available for future grant (in shares) 780,000    
2005 Stock Incentive Plan | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Term of stock option 7 years