Loans and Investments - Schedule of Loan Modifications (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	$ 4,118,117
Deferred interest	29,170
UPB of loan modifications made during 2024	$ 3,970,000
Financing receivable, modified in period, percentage of total investment portfolio	35.00%
Financing receivable, specific reserve	$ 44,300
UPB of loan modifications made during 2023	351,800
Payment Deferrals With/Without Term Extensions
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	$ 2,386,145
Weighted average pay rate	5.99%
Deferred rate	2.06%
Financing receivable modified, weighted average term increase from modification	14 months 12 days
Term Extensions
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	$ 984,372
Financing receivable modified, weighted average term increase from modification	11 months 21 days
Rate Reductions With/Without Term Extensions
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	$ 173,109
Financing receivable modified, weighted average term increase from modification	23 months 18 days
Weighted average interest rate reduction	0.62%
Other
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	$ 574,491
Pay Rate Increase From Time-To-Time
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	379,000
Specific Reserve
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	$ 413,400
Payment Deferrals With Term Extensions
Financing Receivable, Modified [Line Items]
Weighted average pay rate	5.92%
Deferred rate	2.16%
Financing receivable modified, weighted average term increase from modification	14 months 18 days
Financing receivable, modified in period, percentage of total investment portfolio	3.00%
Multifamily
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	$ 4,005,560
Deferred interest	28,600
Multifamily \| Payment Deferrals With/Without Term Extensions
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	2,312,067
Multifamily \| Term Extensions
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	984,372
Multifamily \| Rate Reductions With/Without Term Extensions
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	134,630
Multifamily \| Other
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	574,491
Multifamily \| Payment Deferrals With Term Extensions
Financing Receivable, Modified [Line Items]
Deferred interest	9,945	$ 2,300
UPB of loan modifications, borrowers experiencing financial difficulty during 2023	398,461
Single-Family Rental
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	112,557
Deferred interest	570
Single-Family Rental \| Payment Deferrals With/Without Term Extensions
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	74,078
Single-Family Rental \| Term Extensions
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	0
Single-Family Rental \| Rate Reductions With/Without Term Extensions
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	38,479
Single-Family Rental \| Other
Financing Receivable, Modified [Line Items]
UPB of loan modifications, borrowers experiencing financial difficulty during 2024	$ 0

Financing Receivable, Modified, Deferred Rate

No definition available.

Name:	abr_FinancingReceivableModifiedDeferredRate
Namespace Prefix:	abr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing Receivable, Specific Reserve

+ References

No definition available.

+ Details

Name:	abr_FinancingReceivableSpecificReserve
Namespace Prefix:	abr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of accrued interest on financing receivable modified during period for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-41

+ Details

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

- Definition

Amortized cost excluding accrued interest, of financing receivable 12 months after modification for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestModifiedPast12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

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

- Definition

Percentage, excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty to total financing receivables.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationToTotalFinancingReceivablesExcludingAccruedInterestPercent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
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

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-34

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-33

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

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

- Definition

Accumulated amortized cost of financing receivable modified for debtor experiencing financial difficulty.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 33
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-33

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481746/310-40-50-4

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

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

- Definition

Amortized cost of financing receivable 12 months after modification for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

Name:	us-gaap_FinancingReceivableModifiedPast12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage, after modification, of weighted-average interest rate of financing receivable for debtor experiencing financial difficulty.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 12A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481933/310-10-55-12A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-42

+ Details

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

- Definition

Percentage of decrease in weighted average contractual interest rate of financing receivable modified for debtor experiencing financial difficulty.

+ References

+ Details

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

- Definition

Period of increase in weighted average maturity of financing receivable modified for debtor experiencing financial difficulty, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

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

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=abr_PaymentDeferralWithOrWithoutTermExtensionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_ExtendedMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=abr_ContractualInterestRateReductionWithOrWithoutTermExtensionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=abr_OtherLoanRestructuringModificationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=abr_PaymentDeferralAndPayRateIncreaseFromTimeToTimeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=abr_SpecificReserveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=abr_PaymentDeferralWithExtendedMaturityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=srt_MultifamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=srt_SingleFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: