Income Tax Effect of Each Type of Temporary Difference Comprising Net Deferred Tax Asset (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets:
Net operating losses	$ 85,724	$ 55,086
Stock based compensation	11,660	9,155
Depreciation	(126)	(189)
Tax credits	1,256	5
Other reserves and accrued liabilities	2,900	818
Gross deferred tax asset	101,414	64,875
Less: valuation allowance	(88,999)	(55,894)
Deferred Tax Assets, Net of Valuation Allowance, Total	$ 12,415	$ 8,981

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 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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