Note 10 - Product Warranty Obligations - Recognition of Deferred Revenue Related to Extended Warranties (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Remainder of 2018	$ 3,187
2019	12,941
2020	12,566
2021	10,821
2022	8,502
After 2022	16,904
Total	$ 64,921	$ 63,007	$ 57,854	$ 54,189	$ 43,356	$ 36,139