Common Stock (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended
	Sep. 30, 2011	Dec. 31, 2011 denominator numerator	Oct. 02, 2011 Class A	Dec. 31, 2011 Class A VotePerShare	Aug. 02, 2011 Class A	Dec. 31, 2010 Class A VotePerShare	Dec. 31, 2011 Class B VotePerShare	Dec. 31, 2010 Class B VotePerShare
Common Stock
Common Stock, votes per share				1		1	10	10
Numerator of Common Stock conversion ratio, at the option of the holder		1
Denominator of Common Stock conversion ratio, at the option of the holder		1
Shares of Common Stock reserved for issuance under stock-based compensation plans				3,260,320
Shares of Common Stock reserved for conversion							6,953,680
Number of shares authorized to be repurchased					1,000,000
Number of shares repurchased	1,000,000		1,000,000
Cost of shares repurchased	$ 27.2		$ 27.2