Income Tax Effect of Each Type of Temporary Difference Comprising Net Deferred Tax Asset (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets:
Net operating losses	$ 80,096	$ 85,724
Stock based compensation	15,600	11,660
Depreciation	(90)	(126)
Tax credits	2,141	1,256
Other reserves and accrued liabilities	1,708	2,900
Gross deferred tax asset	99,455us-gaap_DeferredTaxAssetsGross	101,414us-gaap_DeferredTaxAssetsGross
Less: valuation allowance	(85,965)	(88,999)	(55,894)
Deferred Tax Assets, Net of Valuation Allowance, Total	$ 13,490us-gaap_DeferredTaxAssetsNet	$ 12,415us-gaap_DeferredTaxAssetsNet

Deferred Tax Assets, Depreciation and Amortization

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

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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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