Employee Benefit Plans - Deferred Compensation Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined Contribution Plan, Cost Recognized	$ 13.3	$ 10.8	$ 8.5
Supplemental Executive Retirement Plan [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Liability, Current and Noncurrent	28.3	27.9
Compensation expense (reduction in expense)	4.6	4.4	3.9
Deferred Compensation Plan For Select Group Of Employees [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Liability, Current and Noncurrent	46.7	41.1
Compensation expense (reduction in expense)	$ 4.0	$ (1.7)	$ 1.6