Note 3 - Share-based Compensation - Components of Share-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Restricted Stock Units (RSUs) [Member]
Pretax compensation expense	$ 11,250	$ 10,309	$ 38,358	$ 30,942
Tax benefit	2,880	2,660	9,820	7,983
Share unit expense, net of tax	8,370	7,649	28,538	22,959
Performance Shares [Member]
Pretax compensation expense	3,344	3,541	10,300	11,212
Tax benefit	856	914	2,637	2,893
Share unit expense, net of tax	$ 2,488	$ 2,627	$ 7,663	$ 8,319