Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	105,900,000	104,800,000
Treasury stock, shares	9,500,000	9,300,000