Income Tax Effect of Each Type of Temporary Difference Comprising Net Deferred Tax Asset (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Net operating losses	$ 55,086	$ 32,841
Stock based compensation	9,155	5,706
Depreciation	(189)	40
Tax credits	5	6
Other reserves and accrued liabilities	818	53
Net deferred tax asset	64,875	38,646
Less: valuation allowance	(55,894)	(33,379)
Deferred Tax Assets, Net of Valuation Allowance, Total	$ 8,981	$ 5,267

- Definition

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

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- Definition

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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- Definition

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

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- Definition

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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- Definition

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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