Commitments and Contingencies (Details) $ / shares in Units, $ in Millions		1 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares	Nov. 30, 2018 account	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) shares	Jul. 30, 2020 shares
Loss Contingencies [Line Items]
Loss contingency, range of possible loss, portion not accrued	$ 17.2		$ 17.2
Maximum amount of individual accounts receivable account	1.4		1.4
Accrual	$ 5.1		$ 5.1
Common stock outstanding (in shares) | shares	20,796,637		20,796,637	20,303,904
Purchase obligation, due in next twelve months	$ 5,901.5		$ 5,901.5
Purchase obligation, due in second and third year	593.0		593.0
Purchase obligation, due in fourth and fifth year	53.1		53.1
Purchase obligation, due after fifth year	90.3		90.3
Purchase obligation, due in next twelve months	5,689.0		$ 5,689.0
Percentage of stop loss actual estimated claims			120.00%
Self insurance reserve and dental claims	1.9		$ 1.9	$ 1.3
Gain Capital Holdings Inc
Loss Contingencies [Line Items]
Purchase of shareholders equity interest	$ 20.1
Business acquisition, share price (in dollars per share) | $ / shares	$ 6.00		$ 6.00
StoneX Financial
Loss Contingencies [Line Items]
Number of accounts | account		300
Gain Capital Holdings Inc
Loss Contingencies [Line Items]
Common stock outstanding (in shares) | shares	3,400,000		3,400,000		3,600,000