Note 3 - Share-based Compensation (Details Textual) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) shares
Restricted Stock Units (RSUs) [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | $	$ 95.3
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	3 years 1 month 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period (in shares) | shares	10,128
Performance Shares [Member]
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | $	$ 32.3
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	2 years 8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period (in shares) | shares	76,948