Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Income taxes receivable, current	$ 62.4	$ 1.2
Common stock, shares issued (in shares)	51,186,064	50,754,779
Common stock, shares outstanding (in shares)	42,650,599	41,940,089
Common stock, in treasury, shares (in shares)	8,535,465	8,814,690