Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	$ 100,775		$ 100,775
Finite-lived intangible assets, accumulated amortization	(35,048)		(35,048)
Finite-lived intangible assets, carrying value	65,727		65,727
Total identifiable intangible assets, cost	100,807		100,807
Total identifiable intangible assets, carrying value	65,759		65,759		$ 59,259
Amortization expense of intangible assets	2,376	$ 1,800	7,007	$ 5,665
Trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets	32		32
Merchant relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	92,691		92,691
Finite-lived intangible assets, accumulated amortization	(32,365)		(32,365)
Finite-lived intangible assets, carrying value	60,326		$ 60,326
Amortization life			15 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	1,865		$ 1,865
Finite-lived intangible assets, accumulated amortization	(413)		(413)
Finite-lived intangible assets, carrying value	1,452		$ 1,452
Non-compete agreements | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization life			2 years
Non-compete agreements | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization life			3 years
Website development costs
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	18		$ 18
Finite-lived intangible assets, accumulated amortization	(13)		(13)
Finite-lived intangible assets, carrying value	5		$ 5
Amortization life			3 years
Trade names
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	3,717		$ 3,717
Finite-lived intangible assets, accumulated amortization	(1,610)		(1,610)
Finite-lived intangible assets, carrying value	2,107		$ 2,107
Trade names | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization life			2 years
Trade names | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization life			5 years
Residual buyouts
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	1,684		$ 1,684
Finite-lived intangible assets, accumulated amortization	(531)		(531)
Finite-lived intangible assets, carrying value	1,153		$ 1,153
Amortization life			2 years
Referral agreement
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	800		$ 800
Finite-lived intangible assets, accumulated amortization	(116)		(116)
Finite-lived intangible assets, carrying value	$ 684		$ 684
Amortization life			5 years