Note 4 - Revenue From Contracts With Customers - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net revenues	$ 18,062	$ 18,871
Semiconductor Market [Member]
Net revenues	10,111	10,539
Industrial Market [Member]
Net revenues	5,946	5,653
Telecommunications Market [Member]
Net revenues	593	1,279
Other Non-semiconductors Markets [Member]
Net revenues	1,412	1,400
Thermal Testing Products [Member]
Net revenues	5,224	6,032
Induction Heating Products [Member]
Net revenues	5,751	5,622
Semiconductor Production Test Products [Member]
Net revenues	5,284	5,339
Service and Other Products [Member]
Net revenues	1,803	1,878
End User [Member]
Net revenues	16,037	16,328
OEM and Integrators [Member]
Net revenues	$ 2,025	$ 2,543