Share-Based Compensation (Summary of Stock Option Activity) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding at December 31, 2010, shares	1,458,000
Outstanding at December 31, 2010, weighted average exercise price	$ 29.73
Granted, shares	222,000
Granted, weighted average exercise price	$ 42.87
Exercised, shares	(121,900)
Exercised, weighted average exercise price	$ 11.95
Forfeited or Expired, shares	(4,700)
Forfeited or Expired, weighted average exercise price	$ 56.54
Outstanding at December 31, 2011, shares	1,553,400
Outstanding at December 31, 2011, weighted average exercise price	$ 32.92
Exercisable at December 31, 2011, shares	958,000
Exercisable at December 31, 2011, weighted average exercise price	$ 34.58
Exercisable at December 31, 2011, weighted average remaining contractual term, years	5.9
Exercisable at December 31, 2011, average intrinsic value	$ 3.7
Outstanding at December 31, 2010, weighted average remaining contactual term, years	6.9
Outstanding at December 31, 2011, weighted average remaining contactual term, years	6.8
Outstanding at December 31, 2010, aggrefate intrinsic value	17.3
Outstanding at December 31, 2011, aggrefate intrinsic value	4.7
Options expected to vest in the next twelve months, shares	316,500
Options expected to vest in the next twelve months, weighted average exercise price	$ 26.30
Options expected to vest in the next twelve months, weighted average remaining contractual term, years	7.9
Options expected to vest in the next twelve months, agregate intrinsic value	$ 0.9