Condensed Consolidated Income Statements - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Revenues:
Sales of physical commodities	$ 15,864.2	$ 10,804.3	$ 29,783.1	$ 19,687.8
Principal gains, net	323.5	265.2	574.6	468.6
Revenue from contract with customer	970.8	563.1	1,891.5	818.6
Interest income	31.2	23.4	62.2	44.6
Total revenues	16,382.7	11,244.8	30,724.1	20,495.3
Cost of sales of physical commodities	15,838.0	10,773.4	29,728.9	19,643.8
Operating revenues	544.7	471.4	995.2	851.5
Transaction-based clearing expenses	76.5	74.8	147.4	140.2
Introducing broker commissions	43.2	40.8	81.5	79.0
Interest expense	14.1	11.1	29.8	21.0
Interest expense on corporate funding	10.6	10.5	22.4	21.0
Net operating revenues	400.3	334.2	714.1	590.3
Compensation and other expenses:
Compensation and benefits	207.1	185.0	382.1	338.6
Trading systems and market information	16.9	14.8	33.0	28.5
Professional fees	13.8	9.0	25.7	18.3
Non-trading technology and support	12.8	10.6	25.8	21.5
Occupancy and equipment rental	8.8	7.5	17.5	16.1
Selling and marketing	14.3	6.5	25.3	15.3
Travel and business development	3.0	0.5	5.9	1.5
Communications	2.1	2.4	4.0	4.7
Depreciation and amortization	11.3	8.6	20.4	17.0
Bad debt expense, net	12.3	0.9	12.1	2.4
Other	16.9	12.1	28.8	23.2
Total compensation and other expenses	319.3	257.9	580.6	487.1
Other gain	6.4	0.0	6.4	0.0
Income before tax	87.4	76.3	139.9	103.2
Income tax expense	23.4	21.0	34.2	28.4
Net income	$ 64.0	$ 55.3	$ 105.7	$ 74.8
Earnings per share:
Basic (in dollar per shares)	$ 3.18	$ 2.81	$ 5.27	$ 3.81
Diluted (in dollar per shares)	$ 3.11	$ 2.73	$ 5.15	$ 3.71
Weighted-average number of common shares outstanding:
Basic (in shares)	19,573,871	19,112,216	19,477,540	19,025,604
Diluted (in shares)	20,012,709	19,670,539	19,930,047	19,570,028
Commission and clearing fees
Revenues:
Revenue from contract with customer	$ 138.4	$ 129.8	$ 254.7	$ 249.2
Consulting, management, and account fees
Revenues:
Revenue from contract with customer	$ 25.4	$ 22.1	$ 49.5	$ 45.1