Reconciliation of Income Tax Expense (Benefit) (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of Effective Tax Rate [Line Items]
Federal income tax at statutory rates	34.00%	34.00%	34.00%
State income tax, net of federal tax benefit	4.00%	5.00%	6.00%
Research and development credits	9.00%	10.00%	11.00%
Stock compensation	(2.00%)	(1.00%)	(1.00%)
Uncertain tax position adjustment	0.00%	0.00%	0.00%
Change in warrant value	1.00%	2.00%	4.00%
Federal R&D tax grant	0.00%	0.00%	0.00%
Other	0.00%	0.00%	0.00%
Increase in valuation allowance	(46.00%)	(49.00%)	(54.00%)
Effective tax rate	0.00%	0.00%	0.00%