Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	250,000,000	250,000,000
Common stock, shares issued	128,191,000	126,182,000
Common stock, shares outstanding	54,044,000	52,954,000
Treasury stock, shares	74,147,000	73,228,000