Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accumulated depreciation and amortization	$ 555.6	$ 531.6
Preferred stock, par value (in USD per share)	$ 0.01	$ 0.01
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	125,000,000	125,000,000
Common stock, shares, issued (in shares)	37,697,865	37,697,865
Common stock, shares outstanding (in shares)	36,072,347	35,540,233
Treasury stock (in shares)	1,625,518	2,157,632

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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