Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	325,000,000	325,000,000
Common stock, shares issued	121,287,860	120,536,910
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	75,000,000	75,000,000
Preferred stock, shares issued	0	0
Treasury stock at cost, shares	13,728,384	10,068,731