Summary of Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. The condensed consolidated financial statements, including the condensed notes thereto, are unaudited and exclude some of the disclosures required in audited financial statements. Management believes it has made all necessary adjustments, consisting of only normal recurring items, so that the condensed consolidated financial statements are presented fairly and that estimates made in preparing its condensed consolidated financial statements are reasonable and prudent. The accompanying unaudited condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018 filed with the SEC. Certain amounts in the Company’s prior period condensed consolidated financial statements have been reclassified to conform to the current period presentation. The Company has chosen to aggregate certain financial statement line items in the Company’s condensed consolidated statements of operations and condensed consolidated statements of cash flows. Such reclassifications had no effect on total revenues or net loss on the condensed consolidated statements of operations or previously reported totals or subtotals in the condensed consolidated statements of cash flows. The accompanying condensed consolidated financial statements include the accounts of the Company, the Company’s subsidiaries and joint ventures in which the Company has a controlling interest. For consolidated joint ventures, the non-controlling partner’s share of the assets, liabilities and operations of the joint ventures is included in non-controlling interests as equity of the Company. The non-controlling partner’s interest is generally computed as the joint venture partner’s ownership percentage. All intercompany balances and transactions have been eliminated in consolidation. The Company consolidates partially owned entities in which it has a controlling financial interest. In determining whether the Company has a controlling financial interest in a partially owned entity and the requirement to consolidate the accounts of that entity, the Company considers whether the entity is a variable interest entity (“VIE”) and whether it is the primary beneficiary. The Company is the primary beneficiary of a VIE when it has (i) the power to direct the most significant activities impacting the economic performance of the VIE and (ii) the obligation to absorb losses or receive benefits significant to the VIE. BREIT OP and each of the Company’s joint ventures are considered to be a VIE. The Company consolidates these entities because it has the ability to direct the most significant activities of the entities such as purchases, dispositions, financings, budgets, and overall operating plans. As of March 31, 2019, the total assets and liabilities of the Company’s consolidated VIEs, excluding BREIT OP, were $3.6 billion and $2.5 billion, respectively, compared to $2.8 billion and $1.9 billion as of December 31, 2018. Such amounts are included on the Company’s Condensed Consolidated Balance Sheets. The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the balance sheet. Actual results could differ from those estimates.
Fair Value Option	Fair Value Option The Company elected the fair value option (“FVO”) for its investments in term loans. Unrealized gains and losses on the value of financial instruments for which the FVO has been elected are recorded as a component of net income or loss. The Company records any unrealized gains or losses on its investments in term loans as a component of Income from Real Estate-Related Securities and Loans on the Condensed Consolidated Statements of Operations.
Fair Value Measurements	Fair Value Measurements Under normal market conditions, the fair value of an investment is the amount that would be received to sell an asset or transfer a liability in an orderly transaction between market participants at the measurement date (i.e., the exit price). Additionally, there is a hierarchal framework that prioritizes and ranks the level of market price observability used in measuring investments at fair value. Market price observability is impacted by a number of factors, including the type of investment and the characteristics specific to the investment and the state of the marketplace, including the existence and transparency of transactions between market participants. Investments with readily available active quoted prices or for which fair value can be measured from actively quoted prices generally will have a higher degree of market price observability and a lesser degree of judgment used in measuring fair value. Investments measured and reported at fair value are classified and disclosed in one of the following levels within the fair value hierarchy: Level 1 — quoted prices are available in active markets for identical investments as of the measurement date. The Company does not adjust the quoted price for these investments. Level 2 — quoted prices are available in markets that are not active or model inputs are based on inputs that are either directly or indirectly observable as of the measurement date. Level 3 — pricing inputs are unobservable and include instances where there is minimal, if any, market activity for the investment. These inputs require significant judgment or estimation by management or third parties when determining fair value and generally represent anything that does not meet the criteria of Levels 1 and 2. Due to the inherent uncertainty of these estimates, these values may differ materially from the values that would have been used had a ready market for these investments existed. As of March 31, 2019 and December 31, 2018, the Company’s $2.4 billion and $2.3 billion, respectively, of investments in Real Estate-Related Securities and Loans were classified as Level 2. Valuation The Company’s investments in real estate-related securities and loans are reported at fair value. As of March 31, 2019, the Company’s investments in real estate-related securities and loans consisted of commercial mortgage-backed securities (“CMBS”), which are mortgage-related fixed income securities, corporate bonds, and term loans of real estate-related companies. The Company generally determines the fair value of its real estate-related securities and loans by utilizing third-party pricing service providers and broker-dealer quotations on the basis of last available bid price. In determining the fair value of a particular investment, pricing service providers may use broker-dealer quotations, reported trades or valuation estimates from their internal pricing models to determine the reported price. The pricing service providers’ internal models for securities such as real estate-related securities and loans generally consider the attributes applicable to a particular class of the security (e.g., credit rating, seniority), current market data, and estimated cash flows for each class and incorporate deal collateral performance such as prepayment speeds and default rates, as available. As of March 31, 2019, the fair value of the Company’s mortgage notes, term loans, revolving credit facilities, repurchase agreements, and affiliate line of credit was approximately $17.6 million above carrying value. Fair value of the Company’s indebtedness is estimated by modeling the cash flows required by the Company’s debt agreements and discounting them back to the present value using the appropriate discount rate. Additionally, the Company considers current market rates and conditions by evaluating similar borrowing agreements with comparable loan-to-value ratios and credit profiles. The inputs used in determining the fair value of the Company’s indebtedness are considered Level 3.
Stock-Based Compensation	Stock-Based Compensation The Company’s stock-based compensation consists of incentive compensation awards issued to certain employees of affiliate portfolio company service providers. Such awards vest over the life of the awards and stock-based compensation expense is recognized for these awards in net income on a straight-line basis over the applicable vesting period of the award, based on the value of the awards at grant. Refer to Note 10 for additional information.
Recent Accounting Pronouncements	Recent Accounting Pronouncements On January 1, 2019, the Company adopted Accounting Standards Update 2016-02 (“ASU 2016-02”), “Leases,” and all related amendments (codified in Accounting Standards Codification Topic 842 (“Topic 842”)). Certain of the Company’s investments in real estate are subject to ground leases, for which lease liabilities and corresponding right-of-use (“ROU”) assets were recognized as a result of adoption. The Company calculated the amount of the lease liabilities and ROU assets by taking the present value of the remaining lease payments, and adjusted the ROU assets for any existing straight-line ground rent liabilities and acquired ground lease intangibles. The Company’s estimated incremental borrowing rate of a loan with a similar term as the corresponding ground leases was used as the discount rate, which was determined to be approximately 7.0%. Considerable judgment and assumptions were required to estimate the Company’s incremental borrowing rate which was determined by considering the Company’s credit quality, ground lease duration, and debt yields observed in the market. Three of the Company’s existing ground leases were classified as operating leases and upon adoption the Company recognized operating lease liabilities and corresponding ROU assets of $31.3 million. The Company’s existing below-market ground lease intangible asset of $4.5 million, above-market ground lease intangible liability of $4.6 million, and straight-line ground rent liability of $1.2 million were reclassified as of January 1, 2019 to be presented net of the operating ROU assets. In addition, the Company’s existing prepaid ground lease intangible asset of $15.7 million was reclassified as of January 1, 2019 to be presented along with the operating ROU assets. On March 29, 2019, the Company made an acquisition which was subject to ground leases. The present value of the future lease payments under such leases exceeded the fair value of the underlying asset, as such the Company recorded financing lease liabilities and corresponding ROU assets of $56.0 million. The Company’s existing financing ROU asset of $6.1 million is presented along with the acquired financing ROU assets for total ROU assets of $62.1 million as of March 31, 2019. The Company’s financing lease liabilities include the Company’s existing financing lease liability in the amount of $4.3 million. The lease liabilities are included as a component of Accounts Payable, Accrued Expenses, and Other Liabilities and the related ROU assets are recorded as a component of Investments in Real Estate, Net on the Company’s Condensed Consolidated Balance Sheet. Refer to Note 3 and Note 8 for additional information. In transition, the Company elected the package of practical expedients to not reassess (i) whether existing arrangements are or contain a lease, (ii) the classification of an operating or financing lease in a period prior to adoption, and (iii) any initial direct costs for existing leases. Additionally, the Company elected to not use hindsight and carried forward its lease term assumptions when adopting Topic 842 and did not recognize lease liabilities and lease assets for leases with a term of 12 months or less. The Company applied ASU 2016-02 as of the effective date of January 1, 2019 and there was no impact to retained earnings as a result of the Company’s adoption. The adoption of ASU 2016-02 for leases in which the Company is lessor did not have a material impact on the Company’s condensed consolidated financial statements. The Company elected to not separate non-lease components from lease components and presented lease related revenues as a single line item, net of bad debt expense on the Company’s Condensed Consolidated Statement of Operations. Prior to the adoption of ASU 2016-02 the Company separated lease related revenue between “rental revenue” and “tenant reimbursement income” and bad debt expense as a component of “rental property operating” expense. As a result of adoption, the Company reclassified the prior period balances of “tenant reimbursement income” to “rental revenue” to conform to the current period presentation. The Company did not reclassify the prior period balance of bad debt expense on its condensed consolidated statement of operations. The prior period operating lease income presented in “rental revenue” includes $9.0 million previously classified as “tenant reimbursement income” which was determined under the standard in effect prior to the Company’s adoption of ASU 2016-02. Refer to Note 3 for additional information.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2019

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial information and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. The condensed consolidated financial statements, including the condensed notes thereto, are unaudited and exclude some of the disclosures required in audited financial statements. Management believes it has made all necessary adjustments, consisting of only normal recurring items, so that the condensed consolidated financial statements are presented fairly and that estimates made in preparing its condensed consolidated financial statements are reasonable and prudent. The accompanying unaudited condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018 filed with the SEC.

Certain amounts in the Company’s prior period condensed consolidated financial statements have been reclassified to conform to the current period presentation. The Company has chosen to aggregate certain financial statement line items in the Company’s condensed consolidated statements of operations and condensed consolidated statements of cash flows. Such reclassifications had no effect on total revenues or net loss on the condensed consolidated statements of operations or previously reported totals or subtotals in the condensed consolidated statements of cash flows.

The accompanying condensed consolidated financial statements include the accounts of the Company, the Company’s subsidiaries and joint ventures in which the Company has a controlling interest. For consolidated joint ventures, the non-controlling partner’s share of the assets, liabilities and operations of the joint ventures is included in non-controlling interests as equity of the Company. The non-controlling partner’s interest is generally computed as the joint venture partner’s ownership percentage. All intercompany balances and transactions have been eliminated in consolidation.

The Company consolidates partially owned entities in which it has a controlling financial interest. In determining whether the Company has a controlling financial interest in a partially owned entity and the requirement to consolidate the accounts of that entity, the Company considers whether the entity is a variable interest entity (“VIE”) and whether it is the primary beneficiary. The Company is the primary beneficiary of a VIE when it has (i) the power to direct the most significant activities impacting the economic performance of the VIE and (ii) the obligation to absorb losses or receive benefits significant to the VIE. BREIT OP and each of the Company’s joint ventures are considered to be a VIE. The Company consolidates these entities because it has the ability to direct the most significant activities of the entities such as purchases, dispositions, financings, budgets, and overall operating plans.

As of March 31, 2019, the total assets and liabilities of the Company’s consolidated VIEs, excluding BREIT OP, were $3.6 billion and $2.5 billion, respectively, compared to $2.8 billion and $1.9 billion as of December 31, 2018. Such amounts are included on the Company’s Condensed Consolidated Balance Sheets.

The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the balance sheet. Actual results could differ from those estimates.

Fair Value Option

The Company elected the fair value option (“FVO”) for its investments in term loans. Unrealized gains and losses on the value of financial instruments for which the FVO has been elected are recorded as a component of net income or loss. The Company records any unrealized gains or losses on its investments in term loans as a component of Income from Real Estate-Related Securities and Loans on the Condensed Consolidated Statements of Operations.

Fair Value Measurements

Under normal market conditions, the fair value of an investment is the amount that would be received to sell an asset or transfer a liability in an orderly transaction between market participants at the measurement date (i.e., the exit price). Additionally, there is a hierarchal framework that prioritizes and ranks the level of market price observability used in measuring investments at fair value. Market price observability is impacted by a number of factors, including the type of investment and the characteristics specific to the investment and the state of the marketplace, including the existence and transparency of transactions between market participants. Investments with readily available active quoted prices or for which fair value can be measured from actively quoted prices generally will have a higher degree of market price observability and a lesser degree of judgment used in measuring fair value.

Investments measured and reported at fair value are classified and disclosed in one of the following levels within the fair value hierarchy:

Level 1 — quoted prices are available in active markets for identical investments as of the measurement date. The Company does not adjust the quoted price for these investments.

Level 2 — quoted prices are available in markets that are not active or model inputs are based on inputs that are either directly or indirectly observable as of the measurement date.

Level 3 — pricing inputs are unobservable and include instances where there is minimal, if any, market activity for the investment. These inputs require significant judgment or estimation by management or third parties when determining fair value and generally represent anything that does not meet the criteria of Levels 1 and 2. Due to the inherent uncertainty of these estimates, these values may differ materially from the values that would have been used had a ready market for these investments existed.

As of March 31, 2019 and December 31, 2018, the Company’s $2.4 billion and $2.3 billion, respectively, of investments in Real Estate-Related Securities and Loans were classified as Level 2.

Valuation

The Company’s investments in real estate-related securities and loans are reported at fair value. As of March 31, 2019, the Company’s investments in real estate-related securities and loans consisted of commercial mortgage-backed securities (“CMBS”), which are mortgage-related fixed income securities, corporate bonds, and term loans of real estate-related companies. The Company generally determines the fair value of its real estate-related securities and loans by utilizing third-party pricing service providers and broker-dealer quotations on the basis of last available bid price.

In determining the fair value of a particular investment, pricing service providers may use broker-dealer quotations, reported trades or valuation estimates from their internal pricing models to determine the reported price. The pricing service providers’ internal models for securities such as real estate-related securities and loans generally consider the attributes applicable to a particular class of the security (e.g., credit rating, seniority), current market data, and estimated cash flows for each class and incorporate deal collateral performance such as prepayment speeds and default rates, as available.

As of March 31, 2019, the fair value of the Company’s mortgage notes, term loans, revolving credit facilities, repurchase agreements, and affiliate line of credit was approximately $17.6 million above carrying value. Fair value of the Company’s indebtedness is estimated by modeling the cash flows required by the Company’s debt agreements and discounting them back to the present value using the appropriate discount rate. Additionally, the Company considers current market rates and conditions by evaluating similar borrowing agreements with comparable loan-to-value ratios and credit profiles. The inputs used in determining the fair value of the Company’s indebtedness are considered Level 3.

Stock-Based Compensation

The Company’s stock-based compensation consists of incentive compensation awards issued to certain employees of affiliate portfolio company service providers. Such awards vest over the life of the awards and stock-based compensation expense is recognized for these awards in net income on a straight-line basis over the applicable vesting period of the award, based on the value of the awards at grant. Refer to Note 10 for additional information.

Recent Accounting Pronouncements

On January 1, 2019, the Company adopted Accounting Standards Update 2016-02 (“ASU 2016-02”), “Leases,” and all related amendments (codified in Accounting Standards Codification Topic 842 (“Topic 842”)). Certain of the Company’s investments in real estate are subject to ground leases, for which lease liabilities and corresponding right-of-use (“ROU”) assets were recognized as a result of adoption. The Company calculated the amount of the lease liabilities and ROU assets by taking the present value of the remaining lease payments, and adjusted the ROU assets for any existing straight-line ground rent liabilities and acquired ground lease intangibles. The Company’s estimated incremental borrowing rate of a loan with a similar term as the corresponding ground leases was used as the discount rate, which was determined to be approximately 7.0%. Considerable judgment and assumptions were required to estimate the Company’s incremental borrowing rate which was determined by considering the Company’s credit quality, ground lease duration, and debt yields observed in the market.

Three of the Company’s existing ground leases were classified as operating leases and upon adoption the Company recognized operating lease liabilities and corresponding ROU assets of $31.3 million. The Company’s existing below-market ground lease intangible asset of $4.5 million, above-market ground lease intangible liability of $4.6 million, and straight-line ground rent liability of $1.2 million were reclassified as of January 1, 2019 to be presented net of the operating ROU assets. In addition, the Company’s existing prepaid ground lease intangible asset of $15.7 million was reclassified as of January 1, 2019 to be presented along with the operating ROU assets.

On March 29, 2019, the Company made an acquisition which was subject to ground leases. The present value of the future lease payments under such leases exceeded the fair value of the underlying asset, as such the Company recorded financing lease liabilities and corresponding ROU assets of $56.0 million. The Company’s existing financing ROU asset of $6.1 million is presented along with the acquired financing ROU assets for total ROU assets of $62.1 million as of March 31, 2019. The Company’s financing lease liabilities include the Company’s existing financing lease liability in the amount of $4.3 million.

The lease liabilities are included as a component of Accounts Payable, Accrued Expenses, and Other Liabilities and the related ROU assets are recorded as a component of Investments in Real Estate, Net on the Company’s Condensed Consolidated Balance Sheet. Refer to Note 3 and Note 8 for additional information.

In transition, the Company elected the package of practical expedients to not reassess (i) whether existing arrangements are or contain a lease, (ii) the classification of an operating or financing lease in a period prior to adoption, and (iii) any initial direct costs for existing leases. Additionally, the Company elected to not use hindsight and carried forward its lease term assumptions when adopting Topic 842 and did not recognize lease liabilities and lease assets for leases with a term of 12 months or less. The Company applied ASU 2016-02 as of the effective date of January 1, 2019 and there was no impact to retained earnings as a result of the Company’s adoption.

The adoption of ASU 2016-02 for leases in which the Company is lessor did not have a material impact on the Company’s condensed consolidated financial statements. The Company elected to not separate non-lease components from lease components and presented lease related revenues as a single line item, net of bad debt expense on the Company’s Condensed Consolidated Statement of Operations. Prior to the adoption of ASU 2016-02 the Company separated lease related revenue between “rental revenue” and “tenant reimbursement income” and bad debt expense as a component of “rental property operating” expense. As a result of adoption, the Company reclassified the prior period balances of “tenant reimbursement income” to “rental revenue” to conform to the current period presentation. The Company did not reclassify the prior period balance of bad debt expense on its condensed consolidated statement of operations. The prior period operating lease income presented in “rental revenue” includes $9.0 million previously classified as “tenant reimbursement income” which was determined under the standard in effect prior to the Company’s adoption of ASU 2016-02. Refer to Note 3 for additional information.