Employee Benefit Plan (Details) - Savings Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined contribution plan, percentage of employee's contributions matched by employer	50.00%
Defined contribution plan, percentage of employer contribution on employee's earnings	3.00%
Defined contribution plan, employers contribution, rate of vesting, percentage	25.00%
Defined contribution plan, vesting period	4 years
Matching contributions by employer	$ 5.6	$ 5.4	$ 5.3