Income Taxes - Components of Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Stock based compensation	$ 1,524	$ 1,751
Federal and state net operating losses	21,089	12,551
Goodwill	715	826
Accrued compensation	19	51
Deferred rent	344	62
Federal and state research and experimentation credit	3,434	2,322
AMT credit	92	92
Intangible asset differences	253	167
Other	39	74
Total gross deferred tax assets	27,509	17,896
Less valuation allowance	(24,888)	(15,420)
Net deferred tax assets	2,621	2,476
Deferred tax liabilities:
Patent expenditures	(2,012)	(2,017)
Fixed asset differences	(609)	(459)
Total gross deferred tax liabilities	$ (2,621)	$ (2,476)