Property And Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Property, Plant and Equipment [Abstract]
Computer hardware and software	$ 286,380	$ 267,928
Furniture and fixtures	21,145	20,742
Leasehold improvements	47,658	43,769
Gross property and equipment	355,183	332,439
Accumulated depreciation and amortization	(291,583)	(265,326)
Net property and equipment	63,600	67,113	$ 65,162
Depreciation expense	$ 28,000	$ 28,800	$ 28,900