Federal Income Tax Provision Compared With Statutory Rates (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Statutory regular federal income tax rate	(34.00%)	(34.00%)	(34.00%)
Change in valuation allowance	40.20%	37.40%	27.00%
Tax return to prior year provision adjustments			(0.90%)
Reduction of net operating loss attributes			(3.10%)
State tax benefit (net of federal benefit)	(3.10%)	(3.30%)	(4.20%)
Research credits	(3.10%)	(1.90%)	(2.10%)
Foreign amounts with no tax benefit	0.10%	(0.10%)	(0.20%)
Non-deductible expenses	0.40%	1.00%	1.60%
Effect of change in rate	0.90%	2.30%	14.20%
Other	(0.50%)	(0.80%)	0.30%
Total	0.90%	0.60%	(1.40%)