Stock Based Compensation and Share Repurchase Program (Details) (USD $)	1 Months Ended		3 Months Ended
	Feb. 28, 2014	Jul. 31, 2012	Mar. 31, 2014	Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants in period, stock options (in shares)			300,000
Grants in period, restricted share awards (in shares)			300,000
Share based compensation costs			$ 15,100,000	$ 16,400,000
Share Repurchase Program [Abstract]
Authorized amount	1,000,000,000	1,000,000,000
Repurchase Class A Common shares (in shares)			3,106,925	2,394,944
Cost of shares repurchased			250,000,000	150,000,000
Remaining authorization to repurchase shares			1,400,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation costs			5,400,000
Weighted-average period over which unrecognized stock-based compensation costs are expected to be recognized (in years)			1 year 10 months 24 days
Restricted Share Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation costs			$ 38,700,000
Weighted-average period over which unrecognized stock-based compensation costs are expected to be recognized (in years)			2 years 2 months 12 days