Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions		9 Months Ended
		Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net income		$ 109.0	$ 92.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		26.7	12.5
Amortization of right of use assets		6.5	6.0
Bad debts		3.7	6.2
Deferred income taxes		2.2	(0.7)
Amortization of debt issuance costs		2.9	1.3
Amortization of share-based compensation		10.3	7.4
Gain on sale of property and equipment		(0.5)	0.0
Bargain purchase gain on acquisition		(3.3)	0.0
Changes in operating assets and liabilities, net:
Securities and other assets segregated under federal and other regulations		(8.1)	296.2
Securities purchased under agreements to resell		(331.0)	(332.8)
Securities borrowed		(257.3)	(44.2)
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net		(164.1)	55.9
Receivables from clients, net		(217.8)	8.3
Notes receivable, net		(4.9)	(1.8)
Income taxes receivable		(0.5)	7.7
Financial instruments owned, at fair value		(739.5)	(656.7)
Physical commodities inventory, net		(203.7)	(40.9)
Other assets		(13.7)	(7.0)
Accounts payable and other accrued liabilities		35.2	20.5
Operating lease liabilities		(2.4)	(6.7)
Payables to clients		1,488.5	848.4
Payables to broker-dealers, clearing organizations, and counterparties		(162.0)	163.8
Income taxes payable		(6.3)	1.6
Securities sold under agreements to repurchase		472.1	756.7
Securities loaned		258.4	(0.2)
Financial instruments sold, not yet purchased, at fair value		1,078.2	13.5
Net cash provided by operating activities		1,378.6	1,207.2
Cash flows from investing activities:
Cash paid for acquisitions, net		(0.4)	(9.8)
Proceeds from sale of property, plant, and equipment		3.1	0.0
Purchase of property and equipment		(53.5)	(5.5)
Net cash used in investing activities		(50.8)	(15.3)
Cash flows from financing activities:
Net change in payables to lenders under loans with maturities 90 days or less		1.6	150.4
Proceeds from payables to lenders under loans with maturities greater than 90 days		143.4	521.5
Repayments of payables to lenders under loans with maturities greater than 90 days		(148.4)	(560.0)
Proceeds from issuance of senior secured term loan		0.0	21.5
Repayments of senior secured term loan		(7.4)	(7.4)
Proceeds from issuance of senior secured notes		0.0	344.8
Repayment of senior secured notes		(1.6)	0.0
Issuance of note payable		9.0	0.0
Repayments of note payable		0.0	(0.4)
Deferred payments on acquisitions		(1.7)	(0.6)
Repurchase of common stock		(3.1)	(7.5)
Debt issuance costs		0.0	(9.2)
Exercise of stock options		7.6	5.2
Net cash (used in)/provided by financing activities		(0.6)	458.3
Effect of exchange rates on cash, segregated cash, cash equivalents, and segregated cash equivalents		16.7	(2.7)
Net increase in cash, segregated cash, cash equivalents, and segregated cash equivalents		1,343.9	1,647.5
Cash, segregated cash, cash equivalents, and segregated cash equivalents at beginning of period		4,468.4	2,451.3
Cash, segregated cash, cash equivalents, and segregated cash equivalents at end of period		5,812.3	4,098.8
Supplemental disclosure of cash flow information:
Cash paid for interest		58.0	78.0
Income taxes paid, net of cash refunds		44.7	25.7
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions		0.5	11.5
Acquisition of business:
Assets acquired		0.1	357.8
Liabilities assumed		(0.2)	(359.5)
Total net liabilities assumed		(0.1)	(1.7)
Cash and cash equivalents		1,075.6	465.2
Restricted cash held in escrow		0.0	350.0
Cash segregated under federal and other regulations	[1]	2,229.5	1,135.4
Securities segregated under federal and other regulations	[1]	75.0	0.0
Cash segregated and deposited with or pledged to exchange-clearing organizations and other futures commission merchants (“FCMs”)	[2]	2,245.0	1,218.7
Securities segregated and pledged to exchange-clearing organizations	[2]	187.2	929.5
Total cash, segregated cash, cash equivalents, and segregated cash equivalents shown in the condensed consolidated statements of cash flows		5,812.3	4,098.8
Non-cash equivalent segregated assets		21.0	9.8
Non-segregated cash and other non-cash equivalent assets included within deposits and receivables from broker-dealers, clearing organizations, and counterparties		$ 2,185.4	$ 1,248.5

[1] (1) Represents segregated client cash and United States (“U.S.”) Treasury obligations held at third-party banks. Excludes segregated commodity warehouse receipts, segregated U.S. Treasury obligations with original or acquired maturities of greater than 90 days, and other assets of $21.0 million and $9.8 million as of June 30, 2021 and 2020, respectively, included within ‘Cash, securities and other assets segregated under federal and other regulations’ on the Condensed Consolidated Balance Sheets.

[2] (2) Represents segregated client cash and U.S. Treasury obligations on deposit with, or pledged to, exchange clearing organizations and other FCMs. Excludes non-segregated cash, segregated U.S. Treasury obligations pledged to exchange-clearing organizations with original or acquired maturities greater than 90 days, and other assets of $2,185.4 million and $1,248.5 million as of June 30, 2021 and 2020, respectively, included within ‘Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net’ on the Condensed Consolidated Balance Sheets.