Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Sep. 30, 2017
Building
Property, Plant and Equipment [Line Items]
Estimated useful life	30 years
Furniture, equipment, and software development costs | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Furniture, equipment, and software development costs | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years