Condensed Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 7,800	$ 7,700
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
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0005	$ 0.0005
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares issued (in shares)	163,602,067	163,602,067
Treasury stock, common shares (in shares)	74,124,094	73,899,977