Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts receivable, allowance for doubtful accounts	$ 14,037	$ 13,683
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	175,000,000	175,000,000
Common stock, shares issued (in shares)	100,745,077	98,924,501
Common stock, shares outstanding (in shares)	87,081,712	85,261,664
Treasury cost, shares (in shares)	13,663,194	13,663,194