Reconciliation of Effective Tax Rate for the Provision for Income Taxes (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Federal statutory income tax rate	34.00%	34.00%	34.00%
State income taxes, net of federal benefit	11.20%	0.40%	22.80%
Federal and state research credits	2.70%	3.40%	0.80%
Stock based compensation	(1.60%)	(0.20%)	0.40%
Other	(0.10%)	(0.50%)	(0.10%)
Change in valuation allowance	(46.20%)	(37.10%)	(57.90%)
Effective income tax rate	0.00%	0.00%	0.00%

Effective income tax rate reconciliation nondeductible expense share based compensation cost or recovery.

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

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- Definition

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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