Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	6 Months Ended			12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	$ 155,573
Finite-lived intangible assets, accumulated amortization	(52,772)
Finite-lived intangible assets, carrying value	102,801
Total identifiable intangible assets, cost	155,609
Total identifiable intangible assets, carrying value	102,837				$ 107,419
Amortization expense of intangible assets	3,088	$ 3,019	$ 6,282	$ 5,821
Trademarks
Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets	36
Merchant relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	142,671
Finite-lived intangible assets, accumulated amortization	(48,533)
Finite-lived intangible assets, carrying value	$ 94,138
Merchant relationships | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization life	12 years
Merchant relationships | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization life	20 years
Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	$ 1,720
Finite-lived intangible assets, accumulated amortization	(768)
Finite-lived intangible assets, carrying value	$ 952
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	5 years
Website and brand development costs
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	$ 196
Finite-lived intangible assets, accumulated amortization	(38)
Finite-lived intangible assets, carrying value	$ 158
Website and brand development costs | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization life	3 years
Website and brand development costs | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization life	4 years
Trade names
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	$ 4,292
Finite-lived intangible assets, accumulated amortization	(1,788)
Finite-lived intangible assets, carrying value	$ 2,504
Trade names | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization life	2 years
Trade names | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization life	7 years
Residual buyouts
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	$ 5,794
Finite-lived intangible assets, accumulated amortization	(1,296)
Finite-lived intangible assets, carrying value	$ 4,498
Residual buyouts | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization life	2 years
Residual buyouts | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization life	8 years
Referral and exclusivity agreements
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, cost	$ 900
Finite-lived intangible assets, accumulated amortization	(349)
Finite-lived intangible assets, carrying value	$ 551
Referral and exclusivity agreements | Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization life	5 years
Referral and exclusivity agreements | Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization life	10 years