Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 35,244	$ 21,482
Research and development credits	2,597	1,923
License fee	3,339	3,413
Stock Based Compensation	2,291	1,042
Other	1,017	607
Gross deferred tax assets	44,488	28,467
Valuation allowance	(44,440)	(28,448)
Total deferred tax assets	48	19
Deferred tax liabilities:
Other	12	10
Total deferred tax liabilities	12	10
Total net deferred tax assets	$ 36	$ 9