Capital Stock (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Capital Stock (Details)
Common stock, shares authorized	100,000,000
Common stock, par value (in dollars per share)	$ 0.01
Preferred stock, shares authorized	5,000,000
Preferred stock, par value (in dollars per share)	$ 0.01
Common stock, shares outstanding	77,423,415	76,291,745	75,542,282
Treasury stock, shares held	2,249,959	1,533,653	1,497,346
Common Shares Outstanding and Treasury Shares Held Rollforward [Table]
Common shares outstanding, beginning balance	76,291,745	75,542,282	75,258,959
Exercise of common stock options, net	858,727	354,219	204,651
Grants of restricted stock, net	272,943	395,244	78,672
Common shares outstanding, ending balance	77,423,415	76,291,745	75,542,282
Treasury stock, beginning balance	1,533,653	1,497,346	1,582,465
Shares received upon exercise of common stock options	592,992	630	(106,000)
Shares received upon vesting of restricted stock, net	123,314	35,677	20,881
Treasury stock, ending balance	2,249,959	1,533,653	1,497,346
Amount authorized under stock repurchase program	$ 20
Amount repurchased under the stock repurchase program in the period	$ 0