CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Class A common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Class A common stock, shares authorized (in shares)	199,300,000.0	199,300,000.0
Class A common stock, shares issued (in shares)	106,800,000	105,200,000
Class A common stock, shares outstanding (in shares)	89,600,000	88,000,000
Treasury stock, at cost, shares held (in shares)	17,200,000	17,200,000