Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	18,596,774	18,079,522
Common stock, shares outstanding (in shares)	16,726,610	16,253,426
Treasury stock, shares at cost (in shares)	1,870,164	1,826,096
Redeemable Convertible Preferred Stock [Member]
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Redeemable convertible preferred stock, shares authorized (in shares)	100,000,000	100,000,000
Redeemable convertible preferred stock, shares outstanding (in shares)	10,552,941	8,200,000
Preferred stock, liquidation preference	$ 51,170	$ 39,570
Series A Preferred Stock [Member]
Preferred stock, liquidation preference	$ 22,000	$ 22,000