Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for accounts receivable	$ 0.4	$ 0.3
Preferred stock, shares authorized (shares)	50,000,000	50,000,000
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Common stock, shares authorized (shares)	300,000,000	300,000,000
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, shares issued (shares)	42,208,973	42,116,430
Common stock shares outstanding (shares)	42,089,103	42,115,824
Treasury stock, shares	119,870	606