Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Property, plant and equipment, accumulated depreciation and amortization	$ 361.4	$ 323.8
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	60,782,736	60,597,140
Common stock, shares outstanding	52,772,139	54,428,233
Treasury stock, shares	8,010,597	6,168,907