Condensed Consolidated Income Statements - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Revenues:
Revenues	$ 15,047.9	$ 18,930.9	$ 44,220.5	$ 49,655.0
Cost of sales of physical commodities	14,271.0	18,402.1	42,084.4	48,131.0
Operating revenues	776.9	528.8	2,136.1	1,524.0
Transaction-based clearing expenses	66.7	74.7	203.2	222.1
Introducing broker commissions	43.4	41.2	122.4	122.7
Interest expense	216.0	28.1	549.0	57.9
Interest expense on corporate funding	14.9	10.7	44.2	33.1
Net operating revenues	435.9	374.1	1,217.3	1,088.2
Compensation and other expenses:
Compensation and benefits	226.6	202.2	658.1	584.3
Trading systems and market information	19.4	16.0	54.9	49.0
Professional fees	13.9	13.2	41.1	38.9
Non-trading technology and support	13.7	12.9	44.7	38.7
Occupancy and equipment rental	10.0	9.2	29.5	26.7
Selling and marketing	13.7	16.0	40.8	41.3
Travel and business development	6.2	4.9	17.7	10.8
Communications	2.4	2.0	6.7	6.0
Depreciation and amortization	13.8	11.7	39.6	32.1
Bad debts, net of recoveries	6.3	(0.7)	10.0	11.4
Other	15.4	15.8	50.1	44.6
Total compensation and other expenses	341.4	303.2	993.2	883.8
Gain on acquisition and other gain	0.0	0.0	23.5	6.4
Income before tax	94.5	70.9	247.6	210.8
Income tax expense	25.0	21.8	59.8	56.0
Net income	$ 69.5	$ 49.1	$ 187.8	$ 154.8
Earnings per share:
Basic (in dollar per shares)	$ 3.35	$ 2.42	$ 9.12	$ 7.69
Diluted (in dollar per shares)	$ 3.25	$ 2.37	$ 8.82	$ 7.52
Weighted-average number of common shares outstanding:
Basic (in shares)	20,040,167	19,634,450	19,913,424	19,529,843
Diluted (in shares)	20,654,300	20,109,992	20,578,315	19,984,898
Sales of physical commodities
Revenues:
Revenues	$ 14,319.2	$ 18,431.0	$ 42,228.8	$ 48,214.1
Principal gains, net
Revenues:
Revenues	300.0	295.2	810.8	869.8
Commission and clearing fees
Revenues:
Revenues	126.8	126.9	375.5	381.6
Consulting, management, and account fees
Revenues:
Revenues	39.2	27.7	119.7	77.2
Interest income
Revenues:
Revenues	$ 262.7	$ 50.1	$ 685.7	$ 112.3