CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity:
Common stock, par value per share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	99,200,000	99,200,000
Treasury stock, shares (in shares)	45,000,000	44,800,000