Income Taxes - Components of Approximate Deferred Tax (Detail) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Deferred tax assets:    
Net operating loss carryforwards $ 25,085 $ 20,982
Accruals and reserves 1,100 773
Non-qualified stock options 3,357 1,912
Research and development tax credits 989 758
Derivative warrant liability 26 26
Investment in joint venture 251 163
Goodwill 283 23
Fixed assets 78 0
Other 6 6
Total deferred tax assets 31,175 24,643
Less valuation allowance (31,175) (24,558)
Net deferred tax assets 0 85
Deferred tax liabilities:    
Fixed assets 0 (85)
Net deferred taxes $ 0 $ 0