Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income	$ 74.8	$ 55.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	17.0	8.1
Amortization of right of use assets	4.8	3.9
Bad debts	2.4	4.4
Deferred income taxes	4.2	(1.0)
Amortization of debt issuance costs	2.1	0.7
Amortization of share-based compensation	6.5	5.0
Changes in operating assets and liabilities, net:
Securities and other assets segregated under federal and other regulations	(89.6)	297.9
Securities purchased under agreements to resell	(601.0)	164.5
Securities borrowed	(295.3)	359.4
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net	(189.5)	(52.2)
Receivables from clients, net	(78.6)	(63.2)
Notes receivable, net	(5.0)	(1.0)
Income taxes receivable	1.3	8.7
Financial instruments owned, at fair value	(185.4)	(350.5)
Physical commodities inventory, net	(169.7)	(25.9)
Other assets	(22.5)	0.0
Accounts payable and other accrued liabilities	10.0	30.2
Operating lease liabilities	(3.2)	(4.0)
Payables to clients	855.3	942.0
Payables to broker-dealers, clearing organizations, and counterparties	(16.8)	163.0
Income taxes payable	(6.0)	0.1
Securities sold under agreements to repurchase	611.7	26.6
Securities loaned	305.3	(391.1)
Financial instruments sold, not yet purchased, at fair value	432.2	(11.2)
Net cash provided by operating activities	665.0	1,170.0
Cash flows from investing activities:
Cash paid for acquisitions, net	(0.4)	(7.8)
Purchase of property and equipment	(40.0)	(4.5)
Net cash used in investing activities	(40.4)	(12.3)
Cash flows from financing activities:
Net change in payables to lenders under loans with maturities 90 days or less	42.8	111.6
Proceeds from payables to lenders under loans with maturities greater than 90 days	120.4	311.5
Repayments of payables to lenders under loans with maturities greater than 90 days	(125.4)	(350.0)
Proceeds from issuance of senior secured term loan	0.0	21.5
Repayments of senior secured term loan	(4.9)	(4.9)
Issuance of note payable	9.0	0.0
Repayments of note payable	0.0	(0.4)
Deferred payments on acquisitions	(0.8)	(0.2)
Repurchase of common stock	0.0	(7.5)
Debt issuance costs	0.0	(1.5)
Exercise of stock options	5.3	4.0
Net cash provided by financing activities	46.4	84.1
Effect of exchange rates on cash, segregated cash, cash equivalents, and segregated cash equivalents	12.7	(2.7)
Net increase in cash, segregated cash, cash equivalents, and segregated cash equivalents	683.7	1,239.1
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	5,152.1	3,690.4
Supplemental disclosure of cash flow information:
Cash paid for interest	32.9	64.3
Income taxes paid, net of cash refunds	28.2	13.2
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	0.5	7.2
Acquisition of business:
Assets acquired	0.1	352.6
Liabilities assumed	(0.2)	(352.0)
Total net (liabilities)/assets assumed	(0.1)	0.6
Total cash, segregated cash, cash equivalents, and segregated cash equivalents shown in the condensed consolidated statements of cash flows	$ 5,152.1	$ 3,690.4