Stockholders' Equity Share Repurchases (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended			65 Months Ended
	Sep. 30, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Oct. 01, 2018	Apr. 29, 2015	Apr. 29, 2013
Share Repurchases [Line Items]
Issuance of common stock in connection with business and asset acquisitions				$ 16,347
Stock Repurchase Program, Number of Shares Authorized, Value							$ 500,000	$ 500,000
Stock Repurchased and Retired During Period, Shares	5,800,000	8,200,000	9,700,000	5,800,000	64,300,000
Stock Repurchased During Period, Value	$ 99,100	$ 126,900	$ 136,100	$ 99,100	$ 1,070,000
Document Period End Date		Sep. 30, 2019
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets						$ 233,000
Stock Repurchase Program, Remaining Value of Shares Authorized to be Repurchased		$ 430,400
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		3,314	2,963	1,932,286
Payments for Repurchase of Common Stock		$ 126,938	$ 136,090	$ 99,077
Chief Executive Officer [Member]
Share Repurchases [Line Items]
Stock Repurchased and Retired During Period, Shares				1,000,000.0
Stock Repurchased During Period, Value				$ 21,400
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				800,000
Stock Option, Net-settled share equivalent				350,351
Common Stock | Chief Executive Officer [Member]
Share Repurchases [Line Items]
Stock Repurchased and Retired During Period, Shares				649,649
Other Acquisitions [Member]
Share Repurchases [Line Items]
Issuance of common stock in connection with business and asset acquisitions (in shares)			844,108
Issuance of common stock in connection with business and asset acquisitions			$ 13,400