Note 3 - Revenue by Product Group, by Significant Customer and by Geographic Location; Geographic Information - Total Revenue by Geographic Location (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue	$ 26,956	$ 26,787	$ 30,548	$ 21,264	$ 29,388	$ 27,184	$ 33,462	$ 23,386	$ 105,555	$ 113,420	$ 103,379
Percentage of Revenue									100.00%	100.00%	100.00%
UNITED STATES
Revenue									$ 85,351	$ 92,905	$ 83,972
Percentage of Revenue									81.00%	82.00%	81.00%
Europe [Member]
Revenue									$ 11,730	$ 12,435	$ 10,953
Percentage of Revenue									11.00%	11.00%	11.00%
Other Location [Member]
Revenue									$ 8,474	$ 8,080	$ 8,454
Percentage of Revenue									8.00%	7.00%	8.00%