CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares		Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock par value (in dollars per share)	[1]	$ 0.001	$ 0.001
Common stock authorized (in shares)	[1]	199,300,000.0	199,300,000.0
Common stock issued (in shares)	[1]	109,100,000	107,100,000
Common stock outstanding (in shares)	[1]	91,900,000	89,900,000
Treasury stock at cost (in shares)		17,200,000	17,200,000

[1] Following the consummation of the reincorporation merger on January 10, 2018, each authorized, issued and outstanding share of Class A common stock of SGC, par value $0.01 per share, automatically converted into one share of common stock of the surviving corporation, par value $0.001 per share. The change in par value had no impact on total number of authorized, issued and outstanding shares.