Equity-Accounted Investments In Affiliates And Consolidated Funds

No definition available.

Name:	bsig_EquityAccountedInvestmentsInAffiliatesAndConsolidatedFunds
Namespace Prefix:	bsig_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

n/a

+ References

No definition available.

+ Details

Name:	bsig_InvestmentComponentsAbstract
Namespace Prefix:	bsig_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount after accretion (amortization) of discount (premium), and investment expense, of interest income and dividend income on nonoperating securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(a),(b))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

Name:	us-gaap_InvestmentIncomeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_InvestmentIncomeNetAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate amount of income from investments (for example, dividends) not considered a component of the entity's core operations.

+ References

+ Details

Name:	us-gaap_InvestmentIncomeNonoperating
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Sum of the carrying amounts as of the balance sheet date of all investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(h))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

Name:	us-gaap_Investments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_InvestmentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	srt_ConsolidatedEntitiesAxis=bsig_ConsolidatedEntityExcludingConsolidatedFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=bsig_ConsolidatedFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=bsig_OtherDiscretionaryInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=bsig_InvestmentsOfVoluntaryDeferredCompensationPlansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=bsig_EquityAccountedInvestmentsInAffiliatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=bsig_InvestmentsInAffiliatesCarriedAtCostMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Investments - Schedule of Investment Components (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 05, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Investment Components
Investments at fair value		$ 322.4		$ 322.4		$ 321.4
Equity-accounted investments in Affiliates and consolidated Funds		56.2		56.2		1.9
Total investments per Condensed Consolidated Balance Sheets		378.6		378.6		323.3
Investment Income
Net consolidated Funds’ investment gains (losses)		7.0	$ 2.8	25.2	$ 62.8
Investments in unconsolidated Funds
Investment Components
Total investments per Condensed Consolidated Balance Sheets		199.5		199.5		198.5
Investment Income
Investment income		2.3	3.9	11.4	69.6
Consolidated Funds
Investment Components
Investments at fair value		124.6		124.6		124.8
Total investments per Condensed Consolidated Balance Sheets		179.1		179.1		124.8
Investment Income
Net consolidated Funds’ investment gains (losses)		4.7	(1.1)	13.8	(6.8)
Other investments held at fair value \| Investments in unconsolidated Funds
Investment Components
Investments at fair value		102.4		102.4		104.8
Investment Income
Investment income		1.5	3.1	9.3	1.8
Other investments held at fair value \| Consolidated Funds
Investment Income
Net consolidated Funds’ investment gains (losses)		(0.4)	(1.1)	2.6	(6.8)
Investments related to long-term incentive compensation plans held at fair value \| Investments in unconsolidated Funds
Investment Components
Investments at fair value		95.4		95.4		$ 91.8
Investment return of equity-accounted investments in Affiliates \| Investments in unconsolidated Funds
Investment Income
Investment income		0.8	0.8	2.1	2.1
Investment return of equity-accounted investments in Affiliates \| Consolidated Funds
Investment Income
Net consolidated Funds’ investment gains (losses)		5.1	0.0	11.2	0.0
Gain on sale of Affiliate carried at cost \| Investments in unconsolidated Funds
Investment Income
Investment income	$ 65.7	0.0	0.0	0.0	65.7
Gain on sale of Affiliate carried at cost \| Consolidated Funds
Investment Income
Net consolidated Funds’ investment gains (losses)		$ 4.7	$ (1.1)	$ 13.8	$ (6.8)