Annual report pursuant to Section 13 and 15(d)

Income Taxes -Schedule of Effective Income Tax Rate Reconciliation (Detail)

v3.8.0.1
Income Taxes -Schedule of Effective Income Tax Rate Reconciliation (Detail)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Income Tax Contingency [Line Items]    
Tax benefit at federal statutory rate (34.00%) (34.00%)
State income taxes (10.20%) (5.70%)
Permanent differences:    
Stock-based compensation (2.50%) 0.80%
Meals and entertainment 0.10% 0.10%
Change in effective tax rate 39.40%  
Effective income tax rate 0.00% 0.00%
Domestic Tax Authority [Member]    
Permanent differences:    
Effective income tax rate reconciliation, prior year income taxes, percent (2.80%) 1.70%
Effective income tax rate reconciliation, tax credit, research, percent (1.40%) (1.50%)
Effective income tax rate reconciliation, change in deferred tax assets valuation allowance, percent 1.30% 32.90%
State and Local Jurisdiction [Member]    
Permanent differences:    
Effective income tax rate reconciliation, prior year income taxes, percent   1.20%
Effective income tax rate reconciliation, tax credit, research, percent (1.60%) (1.10%)
Effective income tax rate reconciliation, change in deferred tax assets valuation allowance, percent 11.70% 5.60%