Note 4 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Adjustment Amount	$ 200,000
Deferred Tax Liabilities, Foreign Tax Withholding		$ 900,000
Deferred Tax Assets, Valuation Allowance, Total	5,826,000	3,393,000	$ 3,530,000	$ 3,583,000
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	2,400,000	(100,000)
Unrecognized Tax Benefits, Ending Balance	829,000	5,506,000	5,200,000	$ 5,200,000
Unrecognized Tax Benefits, Interest on Income Taxes Expense	100,000	100,000	$ 100,000
Decrease in Unrecognized Tax Benefits is Reasonably Possible	800,000
Minimum [Member]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0
Maximum [Member]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	700,000
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	177,700,000	13,500,000
Domestic Tax Authority [Member] | Created Before 2018 [Member]
Operating Loss Carryforwards, Total	27,000,000
Domestic Tax Authority [Member] | Created in 2018 [Member]
Operating Loss Carryforwards, Total	150,700,000
Domestic Tax Authority [Member] | Expiring Between 2035 and 2038 [Member]
Tax Credit Carryforward, Amount	9,100,000
State and Local Jurisdiction [Member]
Tax Credit Carryforward, Amount	600,000	500,000
Operating Loss Carryforwards, Total	122,300,000	82,900,000
State and Local Jurisdiction [Member] | Expiring in Years 2020 and Forward [Member]
Operating Loss Carryforwards, Total	122,300,000
State and Local Jurisdiction [Member] | Expiring in Years 2019 Through 2028 [Member]
Tax Credit Carryforward, Amount	600,000
Capital Loss Carryforward [Member] | Domestic Tax Authority [Member]
Tax Credit Carryforward, Amount	$ 0	$ 8,700,000