Note 6 - Share-based Compensation - Components of Share-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock Units (RSUs) [Member]
Pretax compensation expense	$ 38,632	$ 32,797	$ 28,679
Tax benefit	9,337	7,740	(4,385)
Share unit expense, net of tax	29,295	25,057	33,064
Performance Shares [Member]
Pretax compensation expense	14,692	14,572	9,612
Tax benefit	3,551	3,439	(1,470)
Share unit expense, net of tax	$ 11,141	$ 11,133	$ 11,082