Credit Facilities - Senior Secured Notes due 2025 (Details) - USD ($)			12 Months Ended
Sep. 01, 2020	Jun. 11, 2020	Sep. 30, 2020
Debt Instrument [Line Items]
Debt instrument, face amount		$ 350,000,000
Debt instrument offering price, percentage		98.50%	8.625%
Debt issuance costs, gross			$ 9,500,000
Debt instrument, redemption price, percentage	100.00%	108.625%	100.00%
Debt instrument, redemption price, percentage of principal amount redeemed			40.00%
Debt instrument remaining outstanding			$ 500,000
Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 91,500,000		$ 100,000,000.0
Debt instrument, redemption price, percentage		100.00%	103.00%
Debt instrument, redemption price, percentage of principal amount redeemed			103.00%
Debt instrument, conversion price (in dollars per share)			$ 6.00
Senior Notes [Member] \| Gain Capital Holdings Inc [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 92,000,000.0
Debt instrument, interest rate, stated percentage			5.00%

Debt Instrument, Discount Rate at Issuance of Face Value

No definition available.

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- Definition

Debt Instrument Remaining Outstanding

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

The price per share of the conversion feature embedded in the debt instrument.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031898-161870

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

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Period Type:	duration

- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

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- Definition

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28555-108399

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Period Type:	instant

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