Income Taxes - Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal income tax at statutory federal rate	35.00%	35.00%	35.00%
State taxes	1.00%	3.10%	4.30%
Permanent differences	(6.40%)	(9.10%)	(2.00%)
Stock-based compensation	(1.30%)	(1.70%)	(0.60%)
Tax credits	21.30%	30.50%	12.40%
Foreign rate differential		(2.30%)	(2.80%)
Change in deferred state tax rate	(2.30%)
Other	(0.50%)	4.50%	(1.50%)
Change in valuation allowance	(46.80%)	(60.00%)	(44.80%)
Effective income tax rate	0.00%	0.00%	0.00%