CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Accounts receivable, allowance (in dollars)	$ 0.0	$ 0.0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	245,000,000	245,000,000
Common stock, shares issued	69,768,128	69,340,985
Common stock, shares outstanding	43,436,076	42,965,856
Treasury stock, shares	26,332,052	26,375,129
Preferred stock
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Series A junior participating preferred stock
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000	100,000
Preferred stock, shares issued	0	0