Income Taxes - Components of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 9,183	$ 35,244
Stock Based Compensation	2,444	2,291
59 (e) expenditures and amortization	1,435
License fee	1,346	3,339
Research and development credits	365	2,597
Other	698	1,017
Gross deferred tax assets	15,471	44,488
Valuation allowance	(15,395)	(44,440)
Total deferred tax assets	76	48
Deferred tax liabilities:
Other	13	12
Total deferred tax liabilities	13	12
Total net deferred tax assets	$ 63	$ 36