Note 2 - Revenue - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue	$ 29,318	$ 26,120	$ 50,688	$ 47,625
Sales Revenue, Net [Member] | Geographic Concentration Risk [Member]
Revenue, percentage	100.00%	100.00%	100.00%	100.00%
UNITED STATES
Revenue	$ 17,696	$ 16,093	$ 31,089	$ 29,629
UNITED STATES | Sales Revenue, Net [Member] | Geographic Concentration Risk [Member]
Revenue, percentage	60.00%	62.00%	61.00%	62.00%
Europe and ROW [Member]
Revenue	$ 2,234	$ 1,914	$ 4,474	$ 3,720
Europe and ROW [Member] | Sales Revenue, Net [Member] | Geographic Concentration Risk [Member]
Revenue, percentage	8.00%	7.00%	9.00%	8.00%
Asia [Member]
Revenue	$ 9,388	$ 8,113	$ 15,125	$ 14,276
Asia [Member] | Sales Revenue, Net [Member] | Geographic Concentration Risk [Member]
Revenue, percentage	32.00%	31.00%	30.00%	30.00%
Product [Member]
Revenue	$ 11,721	$ 10,422	$ 19,656	$ 18,808
Tuberculosis [Member]
Revenue	24,962	21,338	43,799	39,880
Service [Member]
Revenue	17,597	15,698	31,032	28,817
Tick-borne Disease and Other [Member]
Revenue	$ 4,356	$ 4,782	$ 6,889	$ 7,745