Equity (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Equity
Authorized capital stock (in shares)	260,000,000
Authorized shares, par value (in dollars per share)	$ 0.01
Common stock, shares authorized (in shares)	160,000,000	160,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Excess stock, shares authorized (in shares)	75,000,000
Excess stock, par value (in dollars per share)	$ 0.01
Preferred stock, shares authorized (in shares)	25,000,000
Common stock, shares issued (in shares)	87,723,000	81,675,000
Common stock, shares outstanding (in shares)	87,723,000	81,675,000