Annual report pursuant to Section 13 and 15(d)

Federal Income Tax Provision Compared With Statutory Rates (Detail)

v3.8.0.1
Federal Income Tax Provision Compared With Statutory Rates (Detail)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Tax Disclosure [Abstract]      
Statutory regular federal income tax rate (34.00%) (34.00%) (34.00%)
Change in valuation allowance (90.60%) 40.40% 40.20%
State tax benefit (net of federal benefit) (3.20%) (3.00%) (3.10%)
Research credits (1.70%) (3.40%) (3.10%)
Foreign amounts with no tax benefit   0.20% 0.10%
Non-deductible expenses 1.00% 0.60% 0.40%
Effect of change in rate from federal Tax Reform 127.10% 0.50% 0.90%
Other (2.00%) (0.20%) (0.50%)
Total (3.40%) 1.10% 0.90%