Reconciling Items from Income Tax Computed at Statutory Federal Rate (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Federal income tax statutory rate	34.00%	34.00%	34.00%
State income taxes, net of federal benefits	4.10%	4.50%	6.00%
Revalued common and preferred stock warrants		0.90%	(2.30%)
Revalued derivative liability	(1.80%)
Incentive stock option compensation	(1.60%)	(1.90%)	(2.40%)
Research tax credits	1.60%		0.40%
Other	1.90%	(0.10%)	(0.10%)
Valuation allowance	(38.20%)	(37.40%)	(35.60%)
Effective income tax rate	0.00%	0.00%	0.00%