INCOME TAXES - Principal components of deferred tax assets (Details 2) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Depreciation	$ 327	$ 330
Stock compensation	87	103
Federal research and development credits	4,689	4,602
Other	68	36
Total	5,171	5,071
Less valuation allowance	0	0
Deferred tax assets, net	$ 5,171	$ 5,071

Amount before 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 temporary differences from in-process research and development costs expensed in connection with a business combination.

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Amount, before allocation of valuation allowance, of deferred tax asset attributable to deductible tax carryforwards, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from property, plant, and equipment.

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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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