Note 10 - Share-based Compensation - Share-based Compensation Expense (Details) - USD ($)		3 Months Ended		9 Months Ended
	Jan. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based compensation expense	$ 412,000	$ 737,000	$ 756,000	$ 2,333,000	$ 2,142,000
Cost of Goods Sold [Member]
Share-based compensation expense			38,000		130,000
Research and Development Expense [Member]
Share-based compensation expense		357,000	293,000	1,088,000	788,000
Selling, General and Administrative Expenses [Member]
Share-based compensation expense		$ 380,000	$ 425,000	$ 1,245,000	$ 1,224,000