Note 13 - Treasury Stock (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended			54 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Jul. 01, 2015
Treasury Stock, Shares, Ending Balance		172,522	184,497		172,522
Stock Repurchase Program, Authorized Amount						$ 250,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased						600,000
Treasury Stock, Shares, Acquired	5,984				210,631
Treasury Stock, Value, Acquired, Cost Method	$ 5,100	$ 5,073	$ 26,582	$ 528	$ 104,900
Payment, Tax Withholding, Share-based Payment Arrangement		$ 3,017	$ 7,155	$ 4,983
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation		3,521	10,026	7,010