Income Tax Effect of Each Type of Temporary Difference Comprising Net Deferred Tax Asset (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred tax assets:
Net operating losses	$ 32,841	$ 27,171
Stock based compensation	5,706	2,997
Depreciation	40	132
Tax credits	6	30
Other reserves and accrued liabilities	53	422
Net deferred tax asset	38,646	30,752
Less: valuation allowance	(33,379)	(27,978)
Deferred Tax Assets, Net, Total	$ 5,267	$ 2,774

The sum of the tax effects as of the balance sheet date of the amounts of all future tax deductions arising from temporary differences between tax basis and generally accepted accounting principles basis recognition of assets, liabilities, revenues and expenses, which can only be deducted for tax purposes when permitted under enacted tax laws ( before the valuation allowance, if any, to reduce such sum amount to net realizable value). Includes any tax benefit realized in deferred tax assets for significant impacts of tax planning strategies.

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The sum of the tax effects as of the balance sheet date of the amount of excesses of tax deductions over gross income in a year which cannot be used on the tax returns in the current year but can be carried forward to reduce taxable income or income taxes payable in a future year, for which there must be sufficient tax-basis income to utilize a portion or all of the carryforward amount to realize the deferred tax asset.

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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

The tax effect as of the balance sheet date of the amount of the estimated future tax deductions arising from equity-based compensation costs, which can only be deducted for tax purposes when actual costs are incurred, and which can only be realized if sufficient tax-basis income is generated in future periods to enable the deduction to be taken.

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- Definition

The tax effect as of the balance sheet date of the amount of the estimated future tax effects arising from all other reserves, which can only be deducted for tax purposes when losses pertaining to such reserves are actually incurred, and which can only be realized if sufficient tax-basis income is generated in future periods to enable the deduction to be taken.

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- Definition

The sum of the portions of deferred tax assets as of the balance sheet date for which, based on the weight of available evidence, it is more likely than not will not be realized through future reductions of tax-based income.

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