Consolidated Balance Sheets (Parentheticals) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value per share (USD per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value per share (USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	110,000,000	110,000,000
Common stock, shares, issued (in shares)	90,478,075	81,533,548
Treasury stock, shares (in shares)	12,477,780	762,623