Represents the weighted average accrual rate of interest of impaired financing receivables.

No definition available.

Name:	abr_ImpairedFinancingReceivableWeightedAverageAccrualRateOfInterest
Namespace Prefix:	abr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of loans for which the value of the collateral securing the loan was less than the carrying value of the loan for which the entity has not recorded a provision for loan loss.

+ References

No definition available.

+ Details

Name:	abr_NumberOfLoanForWhichNoProvisionForLoanLossMade
Namespace Prefix:	abr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of loans with principal due that have been delinquent.

+ References

No definition available.

+ Details

Name:	abr_NumberOfMortgageLoansOnRealEstateDelinquentPrincipal
Namespace Prefix:	abr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

+ Details

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

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

- Details

Name:	abr_NumberOfLoansUnpaidPrincipalBalanceAxis=abr_SixLoansCollateralizedByLandDevelopmentProjectMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	abr_LoansReceivableMaturityAxis=abr_MaturityDateSeptember2018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	abr_NumberOfLoansUnpaidPrincipalBalanceAxis=abr_FiveLoansCollateralizedByLandDevelopmentProjectMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Investments, Charge-offs and Recoveries Narratives (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($)
Loans and Investments
Number of loans for which no provision for loan loss made \| loan	0		0
Provision for loan losses	$ 63,108	$ 62,783	$ 83,016	$ 83,712
Six loans collateralized by a land development project \| Maturity date of September 2018
Loans and Investments
Unpaid principal balance on loans	$ 120,400
Number of loans with unpaid principal balance \| loan	6
Five loans collateralized by a land development project \| Maturity date of September 2018
Loans and Investments
Unpaid principal balance on loans	$ 111,000
Weighted average accrual rate of interest (as a percent)	8.80%
Provision for loan losses	$ 49,400	$ 49,400
Number of loans with unpaid principal balance \| loan	5