Note 11 - Stock Repurchase Program (Details Textual) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended			41 Months Ended
	Oct. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Sep. 30, 2018	Aug. 31, 2015
Stock Repurchase Program, Authorized Amount	$ 250,000					$ 250,000	$ 200,000
Stock Repurchase Program, Period in Force	2 years
Payments for Repurchase of Common Stock		$ 25,656	$ 30,012	$ 149,937	$ 305,547
Treasury Stock [Member]
Shares Acquired Under Stock Repurchases Program, Shares		560,000	844,500	3,968,706	8,676,706