Commercial Mortgage, Subordinate Loans and Other Lending Assets, Net - Allocation of Carrying Value of Loan Portfolio Based on Internal Risk Ratings (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	75	72
Financing Receivable, before Allowance for Credit Loss	$ 6,488,891,000	$ 6,375,093,000
% of Portfolio	100.00%	100.00%
2020	$ 423,419,000	$ 2,736,825,000
2019	2,609,209,000	1,596,690,000
2018	1,545,407,000	912,636,000
2017	905,895,000	291,700,000
2016	216,777,000	524,246,000
Prior	788,184,000	$ 312,996,000
General CECL Reserves	$ 58,273,000
W.A. Risk Rating	3.1	3.0
1
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	0	0
Financing Receivable, before Allowance for Credit Loss	$ 0	$ 0
% of Portfolio	0.00%	0.00%
2020	$ 0	$ 0
2019	0	0
2018	0	0
2017	0	0
2016	0	0
Prior	$ 0	$ 0
2
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	5	8
Financing Receivable, before Allowance for Credit Loss	$ 130,609,000	$ 348,324,000
% of Portfolio	2.00%	5.50%
2020	$ 0	$ 0
2019	0	241,676,000
2018	23,990,000	0
2017	0	36,250,000
2016	36,287,000	24,546,000
Prior	$ 70,332,000	$ 45,852,000
3
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	63	61
Financing Receivable, before Allowance for Credit Loss	$ 5,822,078,000	$ 5,707,555,000
% of Portfolio	89.70%	89.50%
2020	$ 423,419,000	$ 2,736,825,000
2019	2,609,209,000	1,355,014,000
2018	1,490,045,000	912,636,000
2017	779,882,000	72,540,000
2016	62,580,000	499,700,000
Prior	$ 456,943,000	$ 130,840,000
4
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	0	1
Financing Receivable, before Allowance for Credit Loss	$ 0	$ 182,910,000
% of Portfolio	0.00%	2.90%
2020	$ 0	$ 0
2019	0	0
2018	0	0
2017	0	182,910,000
2016	0	0
Prior	$ 0	$ 0
5
Financing Receivable, Credit Quality Indicator [Line Items]
Number of Loans \| loan	7	2
Financing Receivable, before Allowance for Credit Loss	$ 536,204,000	$ 136,304,000
% of Portfolio	8.30%	2.10%
2020	$ 0	$ 0
2019	0	0
2018	31,372,000	0
2017	126,013,000	0
2016	117,910,000	0
Prior	$ 260,909,000	$ 136,304,000

Loans And Leases Receivable, Number Of Contracts

No definition available.

Name:	ari_LoansAndLeasesReceivableNumberOfContracts
Namespace Prefix:	ari_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Loans And Leases Receivable, Weighted-Average Risk Rating

+ References

No definition available.

+ Details

Name:	ari_LoansAndLeasesReceivableWeightedAverageRiskRating
Namespace Prefix:	ari_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Mortgage Loans on Real Estate, Commercial and Consumer, Percentage of Portfolio

+ References

No definition available.

+ Details

Name:	ari_MortgageLoansOnRealEstateCommercialAndConsumerPercentageOfPortfolio
Namespace Prefix:	ari_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118959141&loc=d3e21338-158488

+ Details

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

- Definition

Amount of financing receivable originated five or more years prior to latest fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=118955255&loc=SL82922352-210448

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919232-210447

+ Details

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

- Definition

Amount of financing receivable originated four years prior to latest fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated in current fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated in fiscal year prior to latest fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919232-210447

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=118955255&loc=SL82922352-210448

+ Details

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

- Definition

Amount of financing receivable originated three years prior to latest fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated two years prior to latest fiscal year.

+ References

+ Details

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

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919230-210447

+ Details

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

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_PassMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_SpecialMentionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_SubstandardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_DoubtfulMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_UnlikelyToBeCollectedFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: