Loans and Investments, Summary of impaired loans (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2017 USD ($) loan	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) loan	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) loan
Loans and Investments
Unpaid Principal Balance	$ 195,085,030		$ 195,085,030		$ 197,640,645
Carrying Value	184,540,050		184,540,050		187,351,035
Allowance for Loan Losses	83,255,922		83,255,922		$ 83,711,575
Average Recorded Investment	195,087,280	$ 196,686,516	196,362,838	$ 197,769,065
Interest Income Recognized	$ 27,728	338,080	$ 472,005	1,061,364
Number of impaired loans \| loan	6		6		8
Land
Loans and Investments
Unpaid Principal Balance	$ 131,085,948		$ 131,085,948		$ 131,085,948
Carrying Value	125,325,106		125,325,106		125,925,677
Allowance for Loan Losses	53,883,478		53,883,478		53,883,478
Average Recorded Investment	131,085,948	130,012,569	131,085,948	128,740,618
Hotel
Loans and Investments
Unpaid Principal Balance	34,750,000		34,750,000		34,750,000
Carrying Value	34,750,000		34,750,000		34,496,296
Allowance for Loan Losses	5,700,000		5,700,000		3,700,000
Average Recorded Investment	34,750,000	34,750,000	34,750,000	34,750,000
Interest Income Recognized		291,542	370,877	857,459
Office
Loans and Investments
Unpaid Principal Balance	27,549,082		27,549,082		27,562,582
Carrying Value	22,764,944		22,764,944		22,778,444
Allowance for Loan Losses	21,972,444		21,972,444		21,972,444
Average Recorded Investment	27,551,332	27,569,332	27,555,832	27,573,832
Interest Income Recognized	27,728	23,601	79,065	69,763
Commercial
Loans and Investments
Unpaid Principal Balance	1,700,000		1,700,000		1,700,000
Carrying Value	1,700,000		1,700,000		1,700,000
Allowance for Loan Losses	1,700,000		1,700,000		1,700,000
Average Recorded Investment	$ 1,700,000	1,700,000	1,700,000	1,700,000
Multifamily
Loans and Investments
Unpaid Principal Balance					2,542,115
Carrying Value					2,450,618
Allowance for Loan Losses					$ 2,455,653
Average Recorded Investment		2,654,615	1,271,058	5,004,615
Interest Income Recognized		$ 22,937	$ 22,063	$ 134,142

The carrying value of impaired financing receivables derived after deducting unearned revenue and other holdbacks.

No definition available.

Name:	abr_ImpairedFinancingReceivablesCarryingAmount
Namespace Prefix:	abr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the number of impaired loans.

+ References

No definition available.

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is a 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 (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

+ Details

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

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

+ Details

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

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=us-gaap_LandAndLandImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=us-gaap_HotelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=us-gaap_OfficeBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=abr_CommercialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=abr_RealEstateMultiFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: