Note 3 - Share-based Compensation - Components of Share-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Restricted Stock Units (RSUs) [Member]
Pretax compensation expense	$ 10,892	$ 9,844	$ 20,634	$ 18,435
Tax benefit	2,723	2,559	5,158	4,793
Share unit expense, net of tax	8,169	7,285	15,476	13,642
Performance Shares [Member]
Pretax compensation expense	3,840	4,121	7,670	7,566
Tax benefit	960	1,071	1,917	1,967
Share unit expense, net of tax	$ 2,880	$ 3,050	$ 5,753	$ 5,599