Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(a)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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 210.9-03.13(1))
-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 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226008-175313

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=49176635&loc=d3e9760-107771

+ Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ari_JPMorganChaseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ari_GeneralFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ari_AssetSpecificFinancingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ari_JPMorganChaseDBRepurchaseFacilityandGoldmanSachsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ari_DeutscheBankRepurchaseFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=ari_GBPLondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ari_GoldmanSachsRepurchaseFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CurrencyAxis=currency_USD
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CurrencyAxis=currency_GBP
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Secured Debt Arrangements, Net - Weighted Average Maturities and Interest Rates of Borrowings (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2018 GBP (£)	Dec. 31, 2017 GBP (£)	Mar. 31, 2017 USD ($)	Mar. 31, 2017 GBP (£)
Debt Instrument [Line Items]
Borrowings outstanding	$ 1,212,749,000	$ 1,330,847,000
less: deferred financing costs	(14,037,000)	(14,348,000)
Line of Credit [Member]
Debt Instrument [Line Items]
Maximum Amount of Borrowings	2,277,906,000	2,290,139,000
Borrowings outstanding	1,212,749,000	1,330,847,000
less: deferred financing costs	(14,037,000)	(14,348,000)
Line of Credit [Member] \| JP Morgan Facility [Member]
Debt Instrument [Line Items]
Maximum Amount of Borrowings	1,382,000,000	1,393,000,000
Borrowings outstanding	800,535,000	$ 944,529,000
Line of Credit [Member] \| JP Morgan Facility [Member] \| General Facility [Member]
Debt Instrument [Line Items]
Line of credit, amount outstanding	1,300,000,000
Line of Credit [Member] \| JP Morgan Facility [Member] \| Asset Specific Financing [Member]
Debt Instrument [Line Items]
Maximum Amount of Borrowings					$ 132,000
Line of credit, amount outstanding	$ 132,000,000
Line of Credit [Member] \| JP Morgan Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.30%	2.30%
Line of Credit [Member] \| JP Morgan Chase, DB Repurchase Facility, and Goldman Sachs [Member]
Debt Instrument [Line Items]
Maximum Amount of Borrowings	$ 2,277,906,000	$ 2,290,139,000
Borrowings outstanding	$ 1,226,786,000	$ 1,345,195,000
Line of Credit [Member] \| JP Morgan Chase, DB Repurchase Facility, and Goldman Sachs [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.35%	2.37%
Line of Credit [Member] \| JP Morgan Chase, DB Repurchase Facility, and Goldman Sachs [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Weighted Average [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.60%	2.60%
Line of Credit [Member] \| Deutsche Bank Repurchase Facility [Member]
Debt Instrument [Line Items]
Maximum Amount of Borrowings					568,200,000
Borrowings outstanding	$ 323,200,000		£ 118,300,000
Line of Credit [Member] \| Deutsche Bank Repurchase Facility [Member] \| General Facility [Member]
Debt Instrument [Line Items]
Maximum Amount of Borrowings					450,000,000	£ 73,300,000
Line of credit, amount outstanding	450,000,000				102,400,000	£ 45,000,000
Line of Credit [Member] \| Deutsche Bank Repurchase Facility [Member] \| Asset Specific Financing [Member]
Debt Instrument [Line Items]
Line of credit, amount outstanding	$ 55,100,000		45,000,000		$ 55,100,000
Line of Credit [Member] \| Deutsche Bank Repurchase Facility [Member] \| GBP London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.60%
Line of Credit [Member] \| Goldman Facility [Member]
Debt Instrument [Line Items]
Maximum Amount of Borrowings	$ 327,750,000	$ 331,130,000
Borrowings outstanding	103,025,000	$ 81,380,000
Line of Credit [Member] \| Goldman Facility [Member] \| General Facility [Member]
Debt Instrument [Line Items]
Borrowings outstanding	75,200,000
Line of credit, amount outstanding	300,000,000
Line of Credit [Member] \| Goldman Facility [Member] \| Asset Specific Financing [Member]
Debt Instrument [Line Items]
Line of credit, amount outstanding	$ 27,800,000
Line of Credit [Member] \| Goldman Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.57%	2.73%
USD \| Line of Credit [Member] \| Deutsche Bank Repurchase Facility [Member]
Debt Instrument [Line Items]
Maximum Amount of Borrowings	$ 402,390,000	$ 472,090,000
Borrowings outstanding	$ 157,460,000	$ 225,367,000
USD \| Line of Credit [Member] \| Deutsche Bank Repurchase Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.48%	2.56%
GBP \| Line of Credit [Member] \| Deutsche Bank Repurchase Facility [Member]
Debt Instrument [Line Items]
Maximum Amount of Borrowings \| £			165,766,000	£ 93,919,000
Borrowings outstanding \| £			£ 165,766,000	£ 93,919,000
GBP \| Line of Credit [Member] \| Deutsche Bank Repurchase Facility [Member] \| GBP London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Weighted Average Rate	2.60%	2.60%