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Agreements and Transactions with Related Parties - Shared Services Agreement (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
ACM | Support Services |  |  |
Agreements and transactions with related parties |  |  |
Costs for services to related party | $ 3.2 | $ 2.4 | $ 2.7

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- Definition Costs of sales and operating expenses for the period incurred from transactions with related parties. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- 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_RelatedPartyTransactionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=abr_ArborCommercialMortgageLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RelatedPartyTransactionAxis=abr_SupportServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |