Commercial Mortgage, Subordinate Loans and Other Lending Assets, Net - CECL Allowance as Percentage of Amortized Cost and Total Commitment (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020
Receivables [Abstract]
CECL Allowance	$ 64,332	$ 30,867
% of Amortized Cost	1.08%	0.49%
Total CECL Allowance	$ 271,313
% of Amortized Cost	4.05%

Allowance For Loan And Lease Losses, Including Loan Specific, Real Estate And Off-Balance Sheet, Credit Loss, Liability, Percent Of Amortized Cost

No definition available.

Name:	ari_AllowanceForLoanAndLeaseLossesIncludingLoanSpecificRealEstateAndOffBalanceSheetCreditLossLiabilityPercentOfAmortizedCost
Namespace Prefix:	ari_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant