Derivatives and Hedging Activities Cash Flow Hedges Text Description (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) contracts	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Loss on Cash Flow Hedge Ineffectiveness	$ 0.0	$ 0.0
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ 0.2
Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Objectives for Using Derivative Instruments	The Company’s objectives in using interest rate derivatives are to add stability to interest income and expense and to manage its exposure to interest rate movements.
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 1,100.0	1,100.0
Not Designated as Hedging Instrument [Member] \| Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	0.2	$ 0.1
Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 100.0
Number of Interest Rate Derivatives Held \| contracts	6
Bank $60m LIBOR Swap 2017 effective 3/22/17 [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 60.0
Objectives for Using Derivative Instruments	The Company’s objectives in using interest rate derivatives are to add stability to interest income and expense and to manage its exposure to interest rate movements.
Derivative, Term of Contract	2 years 3 months
Derivative, Inception Date	Mar. 22, 2017
Derivative, Fixed Interest Rate	1.65%
Bank $60m LIBOR Swap 2017 effective 3/22/17 [Member] \| Weighted Average [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Fixed Interest Rate	1.61%
Bank $40m LIBOR Swap 2017 effective 3/22/17 [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 40.0
Objectives for Using Derivative Instruments	The Company’s objectives in using interest rate derivatives are to add stability to interest income and expense and to manage its exposure to interest rate movements.
Derivative, Term of Contract	1 year 9 months
Derivative, Inception Date	Mar. 22, 2017
Derivative, Fixed Interest Rate	1.55%
Bank $40m LIBOR Swap 2017 effective 3/22/17 [Member] \| Weighted Average [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Fixed Interest Rate	1.61%
Bank $25m LIBOR Swap effective 8/1/13 [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 25.0
Objectives for Using Derivative Instruments	The Company’s objectives in using interest rate derivatives are to add stability to interest income and expense and to manage its exposure to interest rate movements.
Derivative, Inception Date	Aug. 01, 2013
Bank $25m LIBOR Swap effective 8/1/13 [Member] \| Minimum [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Term of Contract	4 years
Derivative, Fixed Interest Rate	1.68%
Bank $25m LIBOR Swap effective 8/1/13 [Member] \| Weighted Average [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Fixed Interest Rate	1.95%
Bank $25m LIBOR Swap effective 8/1/13 [Member] \| Maximum [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Term of Contract	6 years
Derivative, Fixed Interest Rate	2.32%
Bank $25m LIBOR Swap effective 3/1/14 [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 25.0
Objectives for Using Derivative Instruments	The Company’s objectives in using interest rate derivatives are to add stability to interest income and expense and to manage its exposure to interest rate movements.
Derivative, Inception Date	Mar. 01, 2014
Bank $25m LIBOR Swap effective 3/1/14 [Member] \| Minimum [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Term of Contract	4 years
Derivative, Fixed Interest Rate	1.68%
Bank $25m LIBOR Swap effective 3/1/14 [Member] \| Weighted Average [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Fixed Interest Rate	1.95%
Bank $25m LIBOR Swap effective 3/1/14 [Member] \| Maximum [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Term of Contract	6 years
Derivative, Fixed Interest Rate	2.32%
Bank $25m LIBOR Swap 2013 effective 6/1/14 [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 25.0
Objectives for Using Derivative Instruments	The Company’s objectives in using interest rate derivatives are to add stability to interest income and expense and to manage its exposure to interest rate movements.
Derivative, Inception Date	Jun. 01, 2014
Bank $25m LIBOR Swap 2013 effective 6/1/14 [Member] \| Minimum [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Term of Contract	4 years
Derivative, Fixed Interest Rate	1.68%
Bank $25m LIBOR Swap 2013 effective 6/1/14 [Member] \| Weighted Average [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Fixed Interest Rate	1.95%
Bank $25m LIBOR Swap 2013 effective 6/1/14 [Member] \| Maximum [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Term of Contract	6 years
Derivative, Fixed Interest Rate	2.32%
Bank $25m LIBOR Swap effective 9/2/14 [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative Asset, Notional Amount	$ 25.0
Objectives for Using Derivative Instruments	The Company’s objectives in using interest rate derivatives are to add stability to interest income and expense and to manage its exposure to interest rate movements.
Derivative, Inception Date	Sep. 02, 2014
Bank $25m LIBOR Swap effective 9/2/14 [Member] \| Minimum [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Term of Contract	4 years
Derivative, Fixed Interest Rate	1.68%
Bank $25m LIBOR Swap effective 9/2/14 [Member] \| Weighted Average [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Fixed Interest Rate	1.95%
Bank $25m LIBOR Swap effective 9/2/14 [Member] \| Maximum [Member] \| Designated as Hedging Instrument [Member] \| Interest Rate Swap [Member] \| Private Banking Segment [Member]
Derivative [Line Items]
Derivative, Term of Contract	6 years
Derivative, Fixed Interest Rate	2.32%

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

+ Details

Name:	us-gaap_DerivativeAssetNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Date the entity entered into the derivative contract, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeInceptionDates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- 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

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

- Definition

Period the derivative contract is outstanding, 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_DerivativeTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

+ Details

Name:	us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The loss recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

+ Details

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

- Definition

Number of interest rate derivative instruments held by the entity at the reporting date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

+ Details

Name:	us-gaap_NumberOfInterestRateDerivativesHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Description of the reasons for holding or issuing derivative instruments and nonderivative hedging instruments. Includes discussion of the objectives for holding or issuing derivative instruments, the context needed to understand those objectives, and the strategies for achieving those objectives. The description generally distinguishes between derivative and nonderivative instruments by the types of hedging relationships and between those instruments used for risk management purposes and those used for other purposes. Information about those instruments is disclosed in the context of each instrument's primary underlying risk exposure (for example, interest rate, credit, foreign exchange rate, interest rate and foreign exchange rate, or overall price).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84234895&loc=d3e41641-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579240-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84234895&loc=d3e41620-113959

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

+ Details

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

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=bpfh_PrivateBankingSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=bpfh_Bank60mLIBORSwap2017effective32217Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=bpfh_Bank40mLIBORSwap2017effective32217Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=bpfh_Bank25mLIBORSwapeffective8113Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=bpfh_Bank25mLIBORSwapeffective3114Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=bpfh_Bank25mLIBORSwap2013effective6114Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=bpfh_Bank25mLIBORSwapeffective9214Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: