Basis of Financial Statement Presentation (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Common Class A [Member]
Revision of EPS Presentation
Earnings per share, basic	$ 1.25	$ 1.01	$ 3.13	$ 2.75
Earnings per share, diluted	$ 1.02	$ 0.83	$ 2.57	$ 2.26
Common Class A [Member] | As Previously Reported [Member]
Revision of EPS Presentation
Earnings per share, basic	$ 0.83		$ 2.26
Earnings per share, diluted	$ 0.83		$ 2.26
Common Class A [Member] | As Revised [Member]
Revision of EPS Presentation
Earnings per share, basic	$ 1.01		$ 2.75
Earnings per share, diluted	$ 0.83		$ 2.26
Common Class B [Member]
Revision of EPS Presentation
Earnings per share, basic	$ 0.62	$ 0.50	$ 1.57	$ 1.38
Earnings per share, diluted	$ 0.62	$ 0.50	$ 1.57	$ 1.38
Common Class B [Member] | As Previously Reported [Member]
Revision of EPS Presentation
Earnings per share, basic	$ 0.83		$ 2.26
Earnings per share, diluted	$ 0.83		$ 2.26
Common Class B [Member] | As Revised [Member]
Revision of EPS Presentation
Earnings per share, basic	$ 0.50		$ 1.38
Earnings per share, diluted	$ 0.50		$ 1.38