Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Details)

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Stockholders' Equity (Details) (USD $)
In Millions, except Share data, unless otherwise specified
1 Months Ended 9 Months Ended 10 Months Ended 1 Months Ended
Jan. 09, 2012
Class A Common Stock [Member]
Nov. 30, 2011
Class A Common Stock [Member]
Jan. 09, 2012
Class A Common Stock [Member]
Apr. 30, 2011
Class A and Class B Common Stock [Member]
Stockholders' Equity (Textual)        
Maximum authorized repurchase of common stock       $ 500.0
Common stock repurchased, shares 242,700 14,968,488 15,211,188  
Common stock repurchased $ 4.5 $ 281.3 $ 285.8  
Average cost of common stock repurchased $ 18.46 $ 18.79 $ 18.79