Common Stock (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Common Stock [Abstract]
Common stock, shares authorized	150,000,000	150,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares outstanding	96,815,998	97,194,732
Shares available for grant	4,400,000
Stockholder Rights Plan, Right To Purchase Junior Cummulative Preferred Stock, Number Of Shares Per Common Stock	0.01
Stockholder Rights Plan Junior Cummulative Preferred Stock Par Value	$ 0.01
Stockholder rights plan, junior cummulative preferred stock purchase price, per one-hundredth	110.00
Stockholder Rights Plan, Exercise option Minimum Percentage of Common Stock Purchased by Acquirer	20.00%
Stockholder Rights Plan Junior Cummulative Preferred Stock Redemption Price Per Right	0.01
Stock Repurchase Program, Authorized Amount	$ 50.0
Stock Repurchased During Period, Shares	409,007
Stock Repurchased During Period, Value	$ 17.6
Stock Repurchased and Retired During Period, Average Cost Per Share	$ 43.14