Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Net operating loss carryovers	$ 48,912	$ 34,954
Research and development and other tax credits	15,148	8,732
Deferred revenue	1,210	1,919
Intangibles and property and equipment basis difference	2,097	1,874
Stock compensation expense	3,488	1,999
Other	1,129	617
Total deferred tax assets	71,984	50,095
Total deferred tax liabilities	(343)	(1,670)
Net deferred tax asset	71,641	48,425
Valuation allowance	(71,641)	(48,425)
Net deferred tax asset	$ 0	$ 0