Note 6 - Share-based Payments - Amounts of Compensation Expense Recognized Under Stock-based Payment Programs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock compensation expense	$ 1,237	$ 2,148	$ 4,007	$ 3,944
Stock Performance Awards [Member] | Executive Officer [Member]
Stock compensation expense	712	1,418	2,412	2,531
Restricted Stock Units (RSUs) [Member] | Executive Officers and Key Employees [Member]
Stock compensation expense	106	383	785	810
Restricted Stock Units (RSUs) [Member] | Nonemployee Directors [Member]
Stock compensation expense	236	204	440	369
Restricted Stock Units (RSUs) [Member] | Non-executive Employees [Member]
Stock compensation expense	141	143	275	234
Employee Stock Purchase Plan [Member]
Stock compensation expense	$ 42	$ 0	$ 95	$ 0