Income Taxes - Summary of Statutory Federal Tax Rate to Income or Loss before Taxes (Detail)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal tax benefit at statutory rate	34.00%	34.00%	34.00%
Change in valuation allowance	(23.00%)	(42.00%)	(33.00%)
Research and development credits	2.00%	9.00%
Non-deductible warrant	(7.00%)
Foreign loss not benefitted	(5.00%)
Non-deductible expenses and other	(1.00%)	(1.00%)	(1.00%)
Total	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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