Note 2 - Acquisition (Details Textual) - USD ($)		12 Months Ended
	Jul. 22, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Combination, Consideration Transferred	$ 14,200,000
Payments to Acquire Businesses, Gross	11,700,000
Business Combination, Contingent Consideration, Liability	$ 2,500,000
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				$ (2,507,000)
Sensima [Member]
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Business Combination, Contingent Consideration, Liability	$ 2,500,000		$ 0	0
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	$ 8,900,000
Sensima [Member] | Selling, General and Administrative Expenses [Member]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability				$ (2,500,000)