Consolidated Balance Sheets (Parenthetical) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Consolidated Balance Sheets
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	6,000,000	6,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	600,000,000	600,000,000
Common stock, shares issued	212,148,150	209,943,159
Treasury stock, shares	48,359,379	36,555,242