Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		6 Months Ended
	Jun. 09, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2017	Apr. 25, 2017	Feb. 24, 2016
Distribution Made to Limited Partner [Line Items]
Stock Repurchase Program, Authorized Amount					$ 250.0	$ 150.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 78.3	$ 114.6	$ 78.3
Stock Repurchased During Period, Shares		1,000,000	53,721	1,077,029
Stock Repurchased and Retired During Period, Value			$ 7.8	$ 171.7
The Duchossois Group [Member]
Distribution Made to Limited Partner [Line Items]
Stock Repurchased During Period, Shares		1,000,000
Treasury Stock Acquired, Average Cost Per Share	$ 158.78
Stock Repurchased and Retired During Period, Value			$ 158.8