Income Taxes - Significant Components of Net Deferred Tax Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Net operating loss carry forwards	$ 32,143	$ 21,414
Research and development tax credits	2,776	2,414
Accruals and reserves	1,693	47
Depreciation and amortization	33	89
Total deferred tax assets	36,645us-gaap_DeferredTaxAssetsGross	23,964us-gaap_DeferredTaxAssetsGross
Less: Valuation allowance	$ (36,645)	$ (23,964)

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from in-process research and development costs expensed in connection with a business combination.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from reserves and accruals.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Deferred tax asset depreciation and amortization.

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