ACQUISITIONS - Additional Information (Details) $ in Thousands			9 Months Ended	12 Months Ended
	Feb. 01, 2021 USD ($) shares	Nov. 17, 2020 USD ($)	Jun. 30, 2022 USD ($) business	Sep. 30, 2021 USD ($) business
Finite-Lived Intangible Assets [Line Items]
Number of businesses acquired | business				8
2022 Business Combinations
Finite-Lived Intangible Assets [Line Items]
Number of businesses acquired | business			3
Total purchase consideration			$ 107,681
Proceeds from issuance of long-term debt used to fund the acquisition			101,400
Contingent consideration			$ 6,281
Estimated amortization period			15 years
Acquisition-related costs			$ 601
Potential additional consideration			$ 23,000
2022 Business Combinations | Trade name
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period			4 years
2022 Business Combinations | Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period			4 years
2022 Business Combinations | Capitalized software
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period			7 years
2022 Business Combinations | Minimum | Acquired merchant relationships
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period			10 years
2022 Business Combinations | Maximum | Acquired merchant relationships
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period			19 years
BIS
Finite-Lived Intangible Assets [Line Items]
Total purchase consideration	$ 95,495
Proceeds from issuance of long-term debt used to fund the acquisition	$ 52,500
Estimated amortization period	19 years
Acquisition-related costs	$ 374
Potential additional consideration	16,000
Contingent consideration	$ 7,750
BIS | Class A Common Stock
Finite-Lived Intangible Assets [Line Items]
Equity interest issued or issuable, number of shares (in shares) | shares	1,202,914
Common units issued to seller	$ 35,245
BIS | Acquired merchant relationships
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period	19 years
BIS | Trade name
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period	5 years
BIS | Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period	3 years
BIS | Capitalized software
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period	10 years
ImageSoft, Inc.
Finite-Lived Intangible Assets [Line Items]
Total purchase consideration		$ 46,300
Proceeds from issuance of long-term debt used to fund the acquisition		40,000
Contingent consideration		$ 6,300
Estimated amortization period		19 years
Acquisition-related costs		$ 403
Potential additional consideration		$ 20,000
ImageSoft, Inc. | Acquired merchant relationships
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period		20 years
ImageSoft, Inc. | Trade name
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period		5 years
ImageSoft, Inc. | Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period		3 years
ImageSoft, Inc. | Capitalized software
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period		7 years
Other
Finite-Lived Intangible Assets [Line Items]
Number of businesses acquired | business				6
Total purchase consideration				$ 65,527
Proceeds from issuance of long-term debt used to fund the acquisition				$ 57,000
Estimated amortization period				16 years
Acquisition-related costs				$ 1,101
Potential additional consideration				50,200
Contingent consideration				$ 8,527
Other | Proprietary Software and Payments
Finite-Lived Intangible Assets [Line Items]
Number of businesses acquired | business				5
Other | Merchant Services Segment
Finite-Lived Intangible Assets [Line Items]
Number of businesses acquired | business				1
Other | Trade name
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period				4 years
Other | Non-compete agreements
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period				4 years
Other | Capitalized software
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period				7 years
Other | Minimum | Acquired merchant relationships
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period				10 years
Other | Maximum | Acquired merchant relationships
Finite-Lived Intangible Assets [Line Items]
Estimated amortization period				25 years