Note 9 - Stock-based Compensation - Stock-based Compensation Expense and Related Income Tax Benefit (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-based compensation expense, gross	$ 2,000	$ 1,000	$ 5,000	$ 3,000
Income tax benefit at our statutory rate associated with stock-based compensation	(1,000)	0	(1,000)	(1,000)
Stock-based compensation expense, net	$ 1,000	$ 1,000	$ 4,000	$ 2,000