Note 4 - Fair Value Measurements (Details Textual) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Business Combination, Contingent Consideration, Liability, Noncurrent	$ 10,900		$ 10,900		$ 16,800
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	$ (8,000)	$ 700	$ (5,900)	$ 3,300