Note 5 - Stock-based Compensation (Details Textual) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Share-based Payment Arrangement, Nonemployee [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period (in shares)	4
Share-based Payment Arrangement, Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period (in shares)	30
Restricted Stock [Member] | Share-based Payment Arrangement, Nonemployee [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period (in shares)	64	67