Subsequent Events (Details) - $ / shares shares in Thousands	1 Months Ended			3 Months Ended	12 Months Ended
	Oct. 31, 2018	Sep. 30, 2018	Jul. 31, 2018	Sep. 01, 2018	Sep. 03, 2016
Subsequent Event [Line Items]
Cost of repurchase, per share			$ 82.64
Subsequent Event [Member]
Subsequent Event [Line Items]
Shares repurchased and retired	493	7
Cost of repurchase, per share	$ 81.22	$ 85.00
Purchases From Class B Holders [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Shares repurchased and retired	2	113
Cost of repurchase, per share	$ 85.00	$ 84.29
Class A Common Stock [Member]
Subsequent Event [Line Items]
Cost of repurchase, per share				$ 82.64
Class A Common Stock [Member] | Purchases From Class B Holders [Member]
Subsequent Event [Line Items]
Shares repurchased and retired					1,152
Cost of repurchase, per share					$ 72.50