Note 4 - Income Taxes - Deferred Tax Assets And Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net operating loss	$ 73,436	$ 60,268	$ 49,626
Stock option expense	12,169	6,454	5,063
Property and equipment	(14,957)	(11,941)	(10,372)
Other	2,845	1,194	966
Less: Valuation allowance	(73,493)	(55,975)	(45,283)
Net deferred income tax assets	$ 0	$ 0	$ 0

Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, without jurisdictional netting.

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

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