Equity (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Equity
Authorized capital stock (in shares)	260,000,000
Authorized shares, par value (in dollars per share)	$ 0.01
Common stock, shares authorized	160,000,000	160,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Excess stock, shares authorized	75,000,000
Excess stock, par value (in dollars per share)	$ 0.01
Preferred stock, shares authorized	25,000,000
Preferred stock, par value (in dollars per share)	$ 0.01
Common stock, shares issued	94,896,000	89,210,000
Common stock, shares outstanding net of treasury shares	91,249,632