Reconciliation of Income Tax Expense (Benefit) (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	2.00%	4.00%	5.00%
Research and development credits	3.00%	9.00%	10.00%
Stock compensation	(4.00%)	(2.00%)	(1.00%)
Uncertain tax position adjustment	0.00%	0.00%	0.00%
Federal R&D tax grant	0.00%	0.00%	0.00%
Other	(4.00%)	1.00%	2.00%
Increase in valuation allowance	(31.00%)	(46.00%)	(49.00%)
Effective tax rate	0.00%	0.00%	0.00%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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