Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable, allowance for doubtful accounts	$ 13,683	$ 14,799
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)	98,924,501	96,536,251
Common stock, shares outstanding (in shares)	85,261,664	83,256,858
Treasury cost, shares (in shares)	13,663,194	13,279,393