Condensed Consolidated Income Statements - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Revenues:
Principal gains, net	$ 295.2	$ 232.1	$ 869.8	$ 700.7
Revenue from contract with customer	850.6	616.3	2,742.1	1,434.9
Interest income	50.1	27.8	112.3	72.4
Total revenues	18,930.9	10,192.1	49,655.0	30,687.4
Cost of sales of physical commodities	18,402.1	9,760.6	48,131.0	29,404.4
Operating revenues	528.8	431.5	1,524.0	1,283.0
Transaction-based clearing expenses	74.7	67.1	222.1	207.3
Introducing broker commissions	41.2	41.8	122.7	120.8
Interest expense	28.1	14.5	57.9	35.5
Interest expense on corporate funding	10.7	10.1	33.1	31.1
Net operating revenues	374.1	298.0	1,088.2	888.3
Compensation and other expenses:
Compensation and benefits	202.2	177.3	584.3	515.9
Trading systems and market information	16.0	14.4	49.0	42.9
Professional fees	13.2	9.5	38.9	27.8
Non-trading technology and support	12.9	11.3	38.7	32.8
Occupancy and equipment rental	9.2	9.7	26.7	25.8
Selling and marketing	16.0	8.1	41.3	23.4
Travel and business development	4.9	1.3	10.8	2.8
Communications	2.0	2.3	6.0	7.0
Depreciation and amortization	11.7	9.7	32.1	26.7
Bad debt (recovery) expense, net	(0.7)	1.3	11.4	3.7
Other	15.8	10.7	44.6	33.9
Total compensation and other expenses	303.2	255.6	883.8	742.7
Other gain	0.0	3.6	6.4	3.6
Income before tax	70.9	46.0	210.8	149.2
Income tax expense	21.8	11.8	56.0	40.2
Net income	$ 49.1	$ 34.2	$ 154.8	$ 109.0
Earnings per share:
Basic (in dollar per shares)	$ 2.42	$ 1.72	$ 7.69	$ 5.53
Diluted (in dollar per shares)	$ 2.37	$ 1.67	$ 7.52	$ 5.38
Weighted-average number of common shares outstanding:
Basic (in shares)	19,634,450	19,255,452	19,529,843	19,102,244
Diluted (in shares)	20,109,992	19,855,226	19,984,898	19,669,397
Sales of physical commodities
Revenues:
Sales of physical commodities	$ 18,431.0	$ 9,785.9	$ 48,214.1	$ 29,473.7
Commission and clearing fees
Revenues:
Revenue from contract with customer	126.9	124.0	381.6	373.2
Consulting, management, and account fees
Revenues:
Revenue from contract with customer	$ 27.7	$ 22.3	$ 77.2	$ 67.4