Debt Instrument, Redemption Price, Percentage of Accrued or Unpaid Interest

No definition available.

Name:	bsig_DebtInstrumentRedemptionPricePercentageofAccruedorUnpaidInterest
Namespace Prefix:	bsig_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the interest coverage ratio.

+ References

No definition available.

+ Details

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Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- 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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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

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Balance Type:	na
Period Type:	duration

- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after accumulated amortization, of debt discount.

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate amount of interest paid or due on all long-term debt.

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+ Details

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Period Type:	duration

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Borrowings and Debt - Narrative (Details) - USD ($)			1 Months Ended
Borrowings and Debt - Narrative (Details) - USD ($)	Jan. 18, 2022	Feb. 23, 2021	Jul. 31, 2016	Dec. 31, 2021	Dec. 17, 2021	Dec. 31, 2020	Nov. 17, 2020	Sep. 03, 2020	Dec. 31, 2019
Consolidated Entity Excluding Consolidated Funds
Borrowings and debt
Weighted average interest rate				1.60%		2.27%			3.54%
4.80% Senior Notes Due July 27, 2026 \| Senior notes
Borrowings and debt
Contractual face amount			$ 275,000,000	$ 275,000,000
Interest rate (as a percent)				4.80%
Debt instrument, unamortized discount			(500,000)
Debt issuance costs			$ (3,000,000.0)
Contractual term			10 years
Debt instrument, redemption price, percentage			100.00%
Debt instrument, redemption price, percentage of accrued or unpaid interest			0.50%
5.125% Senior Notes Due August 1, 2031 \| Senior notes
Borrowings and debt
Contractual face amount			$ 125,000,000	$ 125,000,000	$ 125,000,000
Interest rate (as a percent)			5.125%	5.125%	5.125%
Debt issuance costs			$ (4,300,000)
Contractual term			15 years
Debt instrument, redemption price, percentage			100.00%
5.125% Senior Notes Due August 1, 2031 \| Senior notes \| Subsequent Event
Borrowings and debt
Debt instrument, redemption price, percentage	101.153%
Debt instrument, percentage of principal amount redeemed	100.00%
Interest expense	$ 1,400,000
Revolving credit facility \| Line of Credit
Borrowings and debt
Contractual face amount		$ 125,000,000		$ 125,000,000		$ 150,000,000	$ 150,000,000	$ 150,000,000
Revolving credit facility \| Line of Credit \| Federal Funds Effective Swap Rate
Borrowings and debt
Variable rate margin (as a percent)		50.00%
Revolving credit facility \| Line of Credit \| LIBOR
Borrowings and debt
Variable rate margin (as a percent)		1.00%
Revolving credit facility \| Line of Credit \| Minimum
Borrowings and debt
Variable rate margin (as a percent)		0.25%
Revolving credit facility \| Line of Credit \| Minimum \| LIBOR
Borrowings and debt
Variable rate margin (as a percent)		150.00%
Revolving credit facility \| Line of Credit \| Maximum
Borrowings and debt
Variable rate margin (as a percent)		0.375%
Revolving credit facility \| Line of Credit \| Maximum \| LIBOR
Borrowings and debt
Variable rate margin (as a percent)		200.00%
Revolving credit facility \| Amended Credit Agreement \| Line of Credit \| Consolidated Entity Excluding Consolidated Funds
Borrowings and debt
Interest coverage ratio		4.0