Note 5 - Warranty and Service Contracts - Summary of Warranties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Balance at beginning of year	$ 2,461	$ 1,819
Add: Accruals for warranties issued during the year	7,583	5,375
Less: Settlements and expirations during the year	(6,536)	(4,733)
Balance at end of year	$ 3,508	$ 2,461