Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Deferred revenue	$ 0	$ 0
Basis difference in equipment	(459)	(587)
Basis difference in intangibles	(6,045)	(8,288)
Accrued liabilities and other	2,246	654
R&D credit	10,980	11,882
AMT credit		79
Stock options	4,360	6,115
Net operating loss carry-forward	64,376	61,660
Gross, Deferred Tax Assets	75,458	71,515
Less: valuation allowance	(75,458)	(71,515)
Net of Valuation Allowance	$ 0	$ 0

Deferred tax assets tax deferred expense reserves and accruals accrued liabilities and other.

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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 from intangible assets including goodwill.

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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 alternative minimum tax credit carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible research tax credit carryforwards.

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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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Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.

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