Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	216,181,636	214,419,155
Common stock, shares outstanding	170,568,534	169,357,084
Preferred stock, shares authorized	30,000,000	30,000,000
Preferred stock, series A convertible preferred stock: shares issued	0	1,600,000
Preferred stock, series A convertible preferred stock: shares outstanding	0	0
Common stock in treasury	45,613,102	45,062,071