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Loans and Investments - Interest Reserves (Details) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2024 USD ($) loan | Dec. 31, 2023 USD ($) loan
Loans and Investments [Abstract] |  |
Interest reserve | $ 200.4 | $ 156.1
Number of loans covered under interest reserve | loan | 588 | 537
Aggregate UPB covered under interest reserve | $ 8,740.0 | $ 8,440.0

X
- Definition Carrying amount as of the balance sheet date pertaining to interest reserve funded to cover debt service costs, based on contractual requirements. + References No definition available. + Details
Name: | abr_InterestReserve
Namespace Prefix: | abr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Number of loans covered under the interest reserve fund. + References No definition available. + Details
Name: | abr_InterestReserveNumberOfLoans
Namespace Prefix: | abr_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of aggregate unpaid principal balance covered under the interest reserve fund. + References No definition available. + Details
Name: | abr_InterestReserveUnpaidPrincipalBalance
Namespace Prefix: | abr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | abr_LoansAndInvestmentsAbstract
Namespace Prefix: | abr_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration