Annual report pursuant to Section 13 and 15(d)

Income Taxes - Summary of Reconciliation of Statutory Income Tax Rate (Detail)

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Income Taxes - Summary of Reconciliation of Statutory Income Tax Rate (Detail)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]      
United States statutory rate 21.00% 34.00% 34.00%
State and local income taxes, net of federal tax benefits 0.70%    
Stock-based compensation 3.60% 0.60% (1.20%)
Deferred rate change 0.30% (12.90%) 0.00%
R&D credit 0.70%   3.50%
Other 0.70%    
Change in valuation allowance (27.00%) (21.70%) (35.20%)
Effective income tax rate 0.00% 0.00% 0.00%