Represents the amount of Equity-accounted investments in affiliates.

No definition available.

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

- Definition

n/a

+ References

No definition available.

+ Details

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Namespace Prefix:	bsig_
Data Type:	xbrli:stringItemType
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- Definition

Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

+ 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 (d)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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- Definition

The net realized gain (loss) on investments sold during the period, not including gains (losses) on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, which, for cash flow reporting, is a component of proceeds from investing activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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- Definition

This element represents the undistributed income (or loss) of equity method investments, net of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporations; such investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities.

+ References

+ Details

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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-Publisher FASB
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-Section S99
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-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

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

- References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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- 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

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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

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

- Definition

The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=bsig_HeitmanLLCMember
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- Details

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- Details

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Investment (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
Investment (Details) - USD ($) $ in Millions	Aug. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment Components
Investments (includes balances reported at fair value of $119.5 and $124.8)		$ 303.8	$ 321.4
Equity-accounted investments in Affiliates		73.1	1.9
Investments		376.9	323.3
Investment income
Gain on sale of Affiliate carried at cost		0.0	65.7	$ 0.0
Heitman LLC
Investment Components
Proceeds from sale of equity method investment	$ 110.0
Consolidated Entity Excluding Consolidated Funds
Investment Components
Investments (includes balances reported at fair value of $119.5 and $124.8)		184.3	196.6
Investments		186.3	198.5
Investment income
Total investment income per Consolidated Statements of Operations		16.8	66.5	27.4
Consolidated Entity Excluding Consolidated Funds \| Other investments held at fair value
Investment Components
Investments (includes balances reported at fair value of $119.5 and $124.8)		95.5	104.8
Consolidated Entity Excluding Consolidated Funds \| Investments related to long-term incentive compensation plans held at fair value
Investment Components
Investments (includes balances reported at fair value of $119.5 and $124.8)		88.8	91.8
Consolidated Entity Excluding Consolidated Funds \| Realized and unrealized gains (losses) on other investments held at fair value
Investment income
Realized and unrealized gains (losses) on consolidated Funds held at fair value		14.0	(1.9)	12.9
Consolidated Entity Excluding Consolidated Funds \| Investment return of equity-accounted investments in Affiliates
Investment income
Investment return of equity-accounted investments		2.8	2.7	14.5
Consolidated Entity Excluding Consolidated Funds \| Gain on sale of Affiliate carried at cost
Investment income
Gain on sale of Affiliate carried at cost		0.0	65.7	0.0
Consolidated Funds
Investment Components
Investments (includes balances reported at fair value of $119.5 and $124.8)		119.5	124.8
Investments		190.6	124.8
Investment income
Realized and unrealized gains (losses) on consolidated Funds held at fair value		4.2	(13.4)	15.5
Investment return of equity-accounted investments		16.7	0.0	0.0
Total investment income per Consolidated Statements of Operations		$ 20.9	$ (13.4)	$ 15.5