Note 3 - Balance Sheet Detail (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Inventory Valuation Reserves, Ending Balance	$ 2,500,000	$ 1,800,000
Property, Plant and Equipment, Net, Ending Balance	2,817,000	2,672,000
Amortization of Intangible Assets, Total	0	0	$ 2,000
Standard Product Warranty Accrual, Ending Balance	6,400,000	7,827,000	$ 3,508,000
Standard Product Warranty Accrual, Decrease for Payments	7,894,000	8,045,000
Product Remediation Liability [Member]
Standard and Extended Product Warranty Accrual, Increase for Warranties Issued, Total		5,000,000
Standard and Extended Product Warranty Accrual, Decrease for Payments, Total		1,100,000
Standard Product Warranty Accrual, Ending Balance	500,000	700,000
Extended Product Warranty Accrual, Ending Balance	2,000,000	3,200,000
Standard Product Warranty Accrual, Decrease for Payments	200,000
Extended Product Warranty Accrual, Decrease for Payments	1,100,000
Vehicles [Member]
Finance Lease, Right-of-Use Asset	2,000,000	1,900,000
Finance Lease, Right-of-Use Asset, Accumulated Amortization	1,100,000	$ 1,100,000
Construction in Progress [Member]
Property, Plant and Equipment, Net, Ending Balance	$ 400,000