Related Party Transactions	12 Months Ended
Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions AMTG Merger As fully described in "Note 19- Business Combination", in August 2016, we acquired AMTG, an entity managed by an affiliate of Apollo. Management Agreement In connection with our initial public offering in September 2009, we entered into a management agreement (the "Management Agreement") with the Manager, which describes the services to be provided by the Manager and its compensation for those services. The Manager is responsible for managing our day-to-day operations, subject to the direction and oversight of our board of directors. Pursuant to the terms of the Management Agreement, the Manager is paid a base management fee equal to 1.5% per annum of our stockholders’ equity (as defined in the Management Agreement), calculated and payable (in cash) quarterly in arrears. The current term of the Management Agreement was renewed during the period and expires on September 29, 2019 and is automatically renewed for successive one-year terms on each anniversary thereafter. The Management Agreement may be terminated upon expiration of the one-year extension term only upon the affirmative vote of at least two-thirds of our independent directors, based upon (1) unsatisfactory performance by the Manager that is materially detrimental to ARI or (2) a determination that the management fee payable to the Manager is not fair, subject to the Manager’s right to prevent such a termination based on unfair fees by accepting a mutually acceptable reduction of management fees agreed to by at least two-thirds of our independent directors. The Manager must be provided with written notice of any such termination at least 180 days prior to the expiration of the then existing term and will be paid a termination fee equal to three times the sum of the average annual base management fee during the 24-month period immediately preceding the date of termination, calculated as of the end of the most recently completed fiscal quarter prior to the date of termination. Following a meeting by our independent directors in February 2018, which included a discussion of the Manager’s performance and the level of the management fees thereunder, we determined not to seek termination of the Management Agreement. For 2018, 2017, and 2016, respectively, we incurred approximately $36.4 million, $31.7 million, and $23.4 million in base management fees under the Management Agreement. In addition to the base management fee, we are also responsible for reimbursing the Manager for certain expenses paid by the Manager on our behalf or for certain services provided by the Manager to us. For 2018, 2017, and 2016, respectively, we paid expenses totaling $3.1 million, $2.6 million, and $2.5 million related to reimbursements for certain expenses paid by the Manager on our behalf under the Management Agreement. Expenses incurred by the Manager and reimbursed by us are reflected in the respective consolidated statement of operations expense category or the consolidated balance sheet based on the nature of the item. Included in payable to related party on the consolidated balance sheet at December 31, 2018 and 2017 are approximately $9.8 million and $8.2 million, respectively, for base management fees incurred but not yet paid under the Management Agreement. Unconsolidated Joint Venture In September 2014, through a wholly owned subsidiary, we acquired a 59% ownership interest in Champ LP. In May 2017, we sold our remaining ownership interest in Champ LP, to unaffiliated third parties. As such, in 2018 we no longer held any interest in Champ LP. Loans receivable In June 2017, we increased our outstanding loan commitment through the acquisition of an additional $25.0 million of interests in an existing subordinate loan from a fund managed by an affiliate of the Manager, increasing our total outstanding loan commitment to $100.0 million. Furthermore, in September 2017 we funded an additional $25.0 million to acquire a portion of the same pre-development subordinate loan from a fund managed by an affiliate of the Manager, increasing our total outstanding loan commitment to $125.0 million. In May 2018, we increased our outstanding principal balance through the acquisition of an additional $28.2 million interest in the same subordinate loan from a fund managed by an affiliate of the Manager. The pre-development subordinate loan is for the construction of a residential condominium building in New York, New York and is part of a $300.0 million subordinate loan. In June 2018, we increased our outstanding loan commitment through the acquisition of £4.8 million ($6.4 million assuming conversion into U.S. dollars) pari-passu interest in an existing subordinate loan from a fund managed by an affiliate of the Manager. The subordinate loan is secured by a healthcare portfolio located in the United Kingdom.

Related Party Transactions

AMTG Merger

As fully described in "Note 19- Business Combination", in August 2016, we acquired AMTG, an entity managed by an affiliate of Apollo.

Management Agreement

In connection with our initial public offering in September 2009, we entered into a management agreement (the "Management Agreement") with the Manager, which describes the services to be provided by the Manager and its compensation for those services. The Manager is responsible for managing our day-to-day operations, subject to the direction and oversight of our board of directors.

Pursuant to the terms of the Management Agreement, the Manager is paid a base management fee equal to 1.5% per annum of our stockholders’ equity (as defined in the Management Agreement), calculated and payable (in cash) quarterly in arrears.

The current term of the Management Agreement was renewed during the period and expires on September 29, 2019 and is automatically renewed for successive one-year terms on each anniversary thereafter. The Management Agreement may be terminated upon expiration of the one-year extension term only upon the affirmative vote of at least two-thirds of our independent directors, based upon (1) unsatisfactory performance by the Manager that is materially detrimental to ARI or (2) a determination that the management fee payable to the Manager is not fair, subject to the Manager’s right to prevent such a termination based on unfair fees by accepting a mutually acceptable reduction of management fees agreed to by at least two-thirds of our independent directors. The Manager must be provided with written notice of any such termination at least 180 days prior to the expiration of the then existing term and will be paid a termination fee equal to three times the sum of the average annual base management fee during the 24-month period immediately preceding the date of termination, calculated as of the end of the most recently completed fiscal quarter prior to the date of termination. Following a meeting by our independent directors in February 2018, which included a discussion of the Manager’s performance and the level of the management fees thereunder, we determined not to seek termination of the Management Agreement.

For 2018, 2017, and 2016, respectively, we incurred approximately $36.4 million, $31.7 million, and $23.4 million in base management fees under the Management Agreement.

In addition to the base management fee, we are also responsible for reimbursing the Manager for certain expenses paid by the Manager on our behalf or for certain services provided by the Manager to us.

For 2018, 2017, and 2016, respectively, we paid expenses totaling $3.1 million, $2.6 million, and $2.5 million related to reimbursements for certain expenses paid by the Manager on our behalf under the Management Agreement. Expenses incurred by the Manager and reimbursed by us are reflected in the respective consolidated statement of operations expense category or the consolidated balance sheet based on the nature of the item.

Included in payable to related party on the consolidated balance sheet at December 31, 2018 and 2017 are approximately $9.8 million and $8.2 million, respectively, for base management fees incurred but not yet paid under the Management Agreement.

Unconsolidated Joint Venture

In September 2014, through a wholly owned subsidiary, we acquired a 59% ownership interest in Champ LP. In May 2017, we sold our remaining ownership interest in Champ LP, to unaffiliated third parties. As such, in 2018 we no longer held any interest in Champ LP.

Loans receivable

In June 2017, we increased our outstanding loan commitment through the acquisition of an additional $25.0 million of interests in an existing subordinate loan from a fund managed by an affiliate of the Manager, increasing our total outstanding loan commitment to $100.0 million. Furthermore, in September 2017 we funded an additional $25.0 million to acquire a portion of the same pre-development subordinate loan from a fund managed by an affiliate of the Manager, increasing our total outstanding loan commitment to $125.0 million. In May 2018, we increased our outstanding principal balance through the acquisition of an additional $28.2 million interest in the same subordinate loan from a fund managed by an affiliate of the Manager. The pre-development subordinate loan is for the construction of a residential condominium building in New York, New York and is part of a $300.0 million subordinate loan.

In June 2018, we increased our outstanding loan commitment through the acquisition of £4.8 million ($6.4 million assuming conversion into U.S. dollars) pari-passu interest in an existing subordinate loan from a fund managed by an affiliate of the Manager. The subordinate loan is secured by a healthcare portfolio located in the United Kingdom.