Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Preferred Stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred Stock, shares authorized	40,000,000	40,000,000
Preferred Stock, shares issued	0	0
Common Stock, par value (usd per share)	$ 0.01	$ 0.01
Common Stock, shares authorized	350,000,000	350,000,000
Common Stock, shares issued	141,051,643	140,040,882
Common Stock, shares outstanding	111,874,453	110,793,855
Treasury Stock, shares	29,177,190	29,247,027