Note 9 - Product Warranty Obligations - Reconciliation of Product Warranty Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Balance at beginning of period	$ 35,422	$ 31,695		$ 30,197
Product warranty reserve assumed in acquisition		43		840
Payments	(20,029)	(18,861)		(18,691)
Provision for warranty issued	26,910	21,347		19,148
Changes in estimates for pre-existing warranties	(518)	1,198		201
Balance at end of period	41,785	35,422		31,695
Balance at beginning of period	57,854	36,139		31,956
Deferred revenue contracts issued	21,440	29,262	[1]	9,797
Amortization of deferred revenue contracts	(10,954)	(7,547)		(5,614)
Balance at end of period	$ 68,340	$ 57,854		$ 36,139

[1] The increase in deferred revenue contracts issued during 2017 was largely due to the launch of a post-sale extended warranty Marketing program.