Stock Based Compensation and Share Repurchase Program (Details) (USD $)	1 Months Ended		3 Months Ended			6 Months Ended	9 Months Ended
	Jul. 31, 2012	Jun. 30, 2011	Sep. 30, 2012	Jun. 30, 2012	Sep. 30, 2011	Jun. 30, 2012	Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period, stock options (in shares)							600,000
Grants in period, restricted share awards (in shares)							400,000
Share based compensation costs			$ 5,500,000		$ 4,800,000		$ 25,300,000	$ 17,400,000
Share Repurchase Program [Abstract]
Authorized amount	1,000,000,000	1,000,000,000
Repurchase Class A Common shares (in shares)				4,600,000		10,100,000	10,133,969	8,870,598
Cost of shares repurchased				250,000,000		500,000,000
Remaining authorization to repurchase shares							1,000,000,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation costs			4,900,000				4,900,000
Weighted-average period over which unrecognized stock-based compensation costs are expected to be recognized (in years)							1.7
Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation costs			$ 20,300,000				$ 20,300,000
Weighted-average period over which unrecognized stock-based compensation costs are expected to be recognized (in years)							1.9