Significant Components of Deferred Tax Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Federal and state net operating loss carryforwards	$ 146,725	$ 102,478
Federal and state research tax credit carryforwards	15,337	10,750
Deferred revenue	12,523us-gaap_DeferredTaxAssetsDeferredIncome	1,755us-gaap_DeferredTaxAssetsDeferredIncome
Stock options	3,776	2,895
Capitalized acquisition costs	1,322	1,295
Other	3,589us-gaap_DeferredTaxAssetsOther	654us-gaap_DeferredTaxAssetsOther
Total deferred tax assets	183,272us-gaap_DeferredTaxAssetsGross	119,827us-gaap_DeferredTaxAssetsGross
Valuation allowance	(183,272)	(119,827)
Net deferred tax assets	$ 0us-gaap_DeferredTaxAssetsNet	$ 0us-gaap_DeferredTaxAssetsNet

Deferred tax assets, capitalized acquisition costs.

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

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

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Amount after 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 operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences not separately disclosed.

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The tax effect as of the balance sheet date of the amount of future tax deductions arising from all unused tax credit carryforwards which have been reduced by a valuation allowance.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from share-based compensation.

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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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