Note 8 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrecognized Tax Benefits, Ending Balance	$ 711,000	$ 525,000	$ 390,000	$ 82,000
Income Tax Expense (Benefit), Total	5,501,000	3,929,000	5,652,000
Deferred Tax Assets, Valuation Allowance, Total	1,255,000	1,991,000
Deferred Tax Assets, Operating Loss Carryforwards, Total	1,421,000	1,898,000
Deferred Tax Assets, Capital Loss Carryforwards	279,000	1,168,000
State and Local Jurisdiction [Member]
Tax Credit Carryforward, Amount	1,400,000
State and Local Jurisdiction [Member] | Internal Revenue Service (IRS) [Member]
Tax Adjustments, Settlements, and Unusual Provisions		200,000
State and Local Jurisdiction [Member] | Spain and Switzerland [Member] | Deferred Tax Assets [Member]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			(300,000)
State and Local Jurisdiction [Member] | Massachusetts [Member] | Tax Credit Carryforwards [Member]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			200,000
Foreign Tax Authority [Member] | AUSTRALIA
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	(700,000)
Deferred Tax Assets, Operating Loss Carryforwards, Total	1,300,000
Deferred Tax Assets, Capital Loss Carryforwards	900,000
Foreign Tax Authority [Member] | FRANCE
Deferred Tax Assets, Operating Loss Carryforwards, Total	2,700,000
Foreign Tax Authority [Member] | SPAIN
Deferred Tax Assets, Operating Loss Carryforwards, Total	900,000
Foreign Tax Authority [Member] | NORWAY
Deferred Tax Assets, Operating Loss Carryforwards, Total	100,000
Foreign Tax Authority [Member] | ITALY
Deferred Tax Assets, Operating Loss Carryforwards, Total	33,000
Foreign Tax Authority [Member] | SWEDEN
Deferred Tax Assets, Operating Loss Carryforwards, Total	4,000
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Tax Adjustments, Settlements, and Unusual Provisions			200,000
Accounting Standards Update 2016-09 [Member]
Income Tax Expense (Benefit), Total	$ (1,100,000)	$ (3,700,000)	$ (300,000)