Capital Stock (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Capital Stock (Details)
Common stock, shares authorized	100,000,000	100,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares outstanding	78,112,032	77,423,415	76,291,745
Treasury stock, shares held	2,334,137	2,249,959	1,533,653
Common Shares Outstanding and Treasury Shares Held Rollforward [Table]
Common shares outstanding, beginning balance	77,423,415	76,291,745	75,542,282
Exercise of common stock options, net	580,097	858,727	354,219
Grants of restricted stock, net	108,520	272,943	395,244
Common shares outstanding, ending balance	78,112,032	77,423,415	76,291,745
Treasury stock, beginning balance	2,249,959	1,533,653	1,497,346
Shares received upon exercise of common stock options	81,616	592,992	630
Shares received upon vesting of restricted stock, net	2,562	123,314	35,677
Treasury stock, ending balance	2,334,137	2,249,959	1,533,653
Amount authorized under stock repurchase program	$ 20
Amount repurchased under the stock repurchase program in the period	$ 0	$ 0	$ 0