Blackstone Mortgage Trust (BXMT) 10-Q 23 Oct 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 16, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	BXMT
Entity Registrant Name	BLACKSTONE MORTGAGE TRUST, INC.
Entity Central Index Key	1,061,630
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		119,669,604

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 86,987	$ 69,654
Restricted cash		32,864
Loans receivable, net	12,176,516	10,056,732
Other assets	155,972	99,575
Total Assets	12,419,475	10,258,825
Liabilities and Equity
Secured debt agreements, net	6,841,759	5,273,855
Loan participations sold, net	81,044	80,415
Securitized debt obligations, net	1,284,362	1,282,412
Convertible notes, net	780,951	563,911
Other liabilities	123,366	140,826
Total Liabilities	9,111,482	7,341,419
Commitments and contingencies
Equity
Class A common stock, $0.01 par value, 200,000,000 shares authorized, 119,669,195 and 107,883,860 shares issued and outstanding as of September 30, 2018 and December 31, 2017, respectively	1,197	1,079
Additional paid-in capital	3,898,841	3,506,861
Accumulated other comprehensive loss	(32,849)	(29,706)
Accumulated deficit	(566,417)	(567,168)
Total Blackstone Mortgage Trust, Inc. stockholders' equity	3,300,772	2,911,066
Non-controlling interests	7,221	6,340
Total Equity	3,307,993	2,917,406
Total Liabilities and Equity	$ 12,419,475	$ 10,258,825

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Billions	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value in dollars per share	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	119,669,195	107,883,860
Common stock, shares outstanding	119,669,195	107,883,860
Variable interest entity, consolidated, carrying amount, assets	$ 1.5	$ 1.5
Variable interest entity, consolidated, carrying amount, liabilities	$ 1.3	$ 1.3

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income from loans and other investments
Interest and related income	$ 203,107	$ 146,446	$ 550,011	$ 391,787
Less: Interest and related expenses	97,955	67,891	255,677	168,917
Income from loans and other investments, net	105,152	78,555	294,334	222,870
Other expenses
Management and incentive fees	18,368	13,243	56,248	40,557
General and administrative expenses	8,443	7,419	25,897	22,219
Total other expenses	26,811	20,662	82,145	62,776
Income before income taxes	78,341	57,893	212,189	160,094
Income tax provision	48	83	272	265
Net income	78,293	57,810	211,917	159,829
Net income attributable to non-controlling interests	(128)	(88)	(481)	(88)
Net income attributable to Blackstone Mortgage Trust, Inc.	$ 78,165	$ 57,722	$ 211,436	$ 159,741
Net income per share of common stock basic and diluted	$ 0.67	$ 0.61	$ 1.90	$ 1.68
Weighted-average shares of common stock outstanding, basic and diluted	116,203,140	95,013,087	111,251,864	95,004,188
Dividends declared per share of common stock	$ 0.62	$ 0.62	$ 1.86	$ 1.86

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net income	$ 78,293	$ 57,810	$ 211,917	$ 159,829
Other comprehensive income
Unrealized (loss) gain on foreign currency remeasurement	(2,416)	16,175	(26,766)	43,990
Realized and unrealized gain (loss) on derivative financial instruments	1,703	(8,029)	23,623	(20,150)
Other comprehensive (loss) income	(713)	8,146	(3,143)	23,840
Comprehensive income	77,580	65,956	208,774	183,669
Comprehensive income attributable to non-controlling interests	(128)	(88)	(481)	(88)
Comprehensive income attributable to Blackstone Mortgage Trust, Inc.	$ 77,452	$ 65,868	$ 208,293	$ 183,581

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Class A Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Accumulated Deficit [Member]	Stockholders' Equity [Member]	Non-Controlling Interests [Member]
Balance at Dec. 31, 2016	$ 2,493,603	$ 945	$ 3,089,997	$ (56,202)	$ (541,137)	$ 2,493,603
Shares of class A common stock issued, net	3	3				3
Restricted class A common stock earned	17,493		17,493			17,493
Issuance of convertible notes	964		964			964
Dividends reinvested	31		327		(296)	31
Deferred directors' compensation	313		313			313
Other comprehensive income	23,840			23,840		23,840
Net income	159,829				159,741	159,741	$ 88
Dividends declared on common stock	(176,374)				(176,374)	(176,374)
Contributions to non-controlling interests	6,090						6,090
Balance at Sep. 30, 2017	2,525,792	948	3,109,094	(32,362)	(558,066)	2,519,614	6,178
Balance at Dec. 31, 2017	2,917,406	1,079	3,506,861	(29,706)	(567,168)	2,911,066	6,340
Shares of class A common stock issued, net	369,790	118	369,672			369,790
Restricted class A common stock earned	20,110		20,110			20,110
Issuance of convertible notes	1,462		1,462			1,462
Conversion of convertible notes	(20)		(20)			(20)
Dividends reinvested	39		381		(342)	39
Deferred directors' compensation	375		375			375
Other comprehensive income	(3,143)			(3,143)		(3,143)
Net income	211,917				211,436	211,436	481
Dividends declared on common stock	(210,343)				(210,343)	(210,343)
Contributions from non-controlling interests	4,500						4,500
Distributions to non-controlling interests	(4,100)						(4,100)
Balance at Sep. 30, 2018	$ 3,307,993	$ 1,197	$ 3,898,841	$ (32,849)	$ (566,417)	$ 3,300,772	$ 7,221

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net income	$ 211,917	$ 159,829
Adjustments to reconcile net income to net cash provided by operating activities
Non-cash compensation expense	20,488	17,809
Amortization of deferred fees on loans and debt securities	(35,955)	(28,887)
Amortization of deferred financing costs and premiums/ discount on debt obligations	20,993	16,356
Changes in assets and liabilities, net
Other assets	(9,709)	(219)
Other liabilities	15,001	11,651
Net cash provided by operating activities	222,735	176,539
Cash flows from investing activities
Origination and fundings of loans receivable	(5,222,803)	(2,314,721)
Principal collections and sales proceeds from loans receivable	2,503,454	1,976,271
Loan contributed to securitization	512,002
Investment in debt securities held-to-maturity	(95,937)
Origination and exit fees received on loans receivable	74,111	38,434
Receipts under derivative financial instruments	34,975	6,115
Payments under derivative financial instruments	(14,031)	(18,115)
Return of collateral deposited under derivative agreements	28,870	8,980
Collateral deposited under derivative agreements	(32,110)	(16,651)
Net cash used in investing activities	(2,211,469)	(319,687)
Cash flows from financing activities
Borrowings under secured debt agreements	5,749,678	2,776,058
Repayments under secured debt agreements	(4,147,893)	(2,481,250)
Proceeds from sale of loan participations	86,339	33,193
Repayment of loan participations	(85,875)	(381,310)
Payment of deferred financing costs	(18,995)	(13,591)
Contributions from non-controlling interests	4,500	6,090
Distributions to non-controlling interests	(4,100)
Net proceeds from issuance of convertible notes	214,775	394,074
Repayment of convertible notes	(192)
Net proceeds from issuance of class A common stock	369,787	31
Dividends paid on class A common stock	(203,065)	(176,195)
Net cash provided by financing activities	1,964,959	157,100
Net decrease in cash, cash equivalents, and restricted cash	(23,775)	13,952
Cash, cash equivalents, and restricted cash at beginning of period	102,518	75,567
Effects of currency translation on cash, cash equivalents, and restricted cash	8,244	4,566
Cash, cash equivalents, and restricted cash at end of period	86,987	94,085
Supplemental disclosure of cash flows information
Payments of interest	(224,320)	(141,124)
Payments of income taxes	(546)	(220)
Supplemental disclosure of non-cash investing and financing activities
Dividends declared, not paid	(74,195)	(58,793)
Loan principal payments held by servicer, net	$ 3,577	513
Consolidation of loans receivable of a VIE		500,000
Consolidation of securitized debt obligations of a VIE		$ (474,620)

Organization

Organization	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	1. ORGANIZATION References herein to “Blackstone Mortgage Trust,” “Company,” “we,” “us” or “our” refer to Blackstone Mortgage Trust, Inc. and its subsidiaries unless the context specifically requires otherwise. Blackstone Mortgage Trust is a real estate finance company that originates senior loans collateralized by commercial real estate in North America, Europe, and Australia. Our investment objective is to preserve and protect shareholder capital while producing attractive risk-adjusted returns primarily through dividends generated from current income from our loan portfolio. We are externally managed by BXMT Advisors L.L.C., or our Manager, a subsidiary of The Blackstone Group L.P., or Blackstone, and are a real estate investment trust, or REIT, traded on the New York Stock Exchange, or NYSE, under the symbol “BXMT.” Our principal executive offices are located at 345 Park Avenue, 42 nd We conduct our operations as a REIT for U.S. federal income tax purposes. We generally will not be subject to U.S. federal income taxes on our taxable income to the extent that we annually distribute all of our net taxable income to stockholders and maintain our qualification as a REIT. We also operate our business in a manner that permits us to maintain an exclusion from registration under the Investment Company Act of 1940, as amended. We are organized as a holding company and conduct our business primarily through our various subsidiaries.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES The accompanying unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America, or GAAP, for interim financial information and the instructions to Form 10-Q 10-01 S-X. 10-K Basis of Presentation The accompanying consolidated financial statements include, on a consolidated basis, our accounts, the accounts of our wholly-owned subsidiaries, majority-owned subsidiaries, and variable interest entities, or VIEs, of which we are the primary beneficiary. All intercompany balances and transactions have been eliminated in consolidation. Principles of Consolidation We consolidate all entities that we control through either majority ownership or voting rights. In addition, we consolidate all VIEs of which we are considered the primary beneficiary. VIEs are defined as entities in which equity investors (i) do not have the characteristics of a controlling financial interest and/or (ii) do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties. The entity that consolidates a VIE is known as its primary beneficiary and is generally the entity with (i) the power to direct the activities that most significantly affect the VIE’s economic performance and (ii) the right to receive benefits from the VIE or the obligation to absorb losses of the VIE that could be significant to the VIE. In the third quarter of 2018, we contributed a loan to a single asset securitization vehicle, or the 2018 Single Asset Securitization, which is a VIE, and invested in the related subordinate risk retention position. We are not the primary beneficiary of the VIE because we do not have the power to direct the activities that most significantly affect the VIE’s economic performance and, therefore, do not consolidate the 2018 Single Asset Securitization on our balance sheet. We have classified the subordinate risk retention position as a held-to-maturity In April 2017, we entered into a joint venture, or our Multifamily Joint Venture, with Walker & Dunlop Inc. to originate, hold, and finance multifamily bridge loans. Pursuant to the terms of the agreements governing the joint venture, Walker & Dunlop contributed 15% of the venture’s equity capital and we contributed 85%. We consolidate the Multifamily Joint Venture as we have a controlling financial interest. The non-controlling non-controlling Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may ultimately differ from those estimates. Revenue Recognition Interest income from our loans receivable portfolio and debt securities is recognized over the life of each investment using the effective interest method and is recorded on the accrual basis. Recognition of fees, premiums, and discounts associated with these investments is deferred and recorded over the term of the loan or debt security as an adjustment to yield. Income accrual is generally suspended for loans at the earlier of the date at which payments become 90 days past due or when, in the opinion of our Manager, recovery of income and principal becomes doubtful. Income is then recorded on the basis of cash received until accrual is resumed when the loan becomes contractually current and performance is demonstrated to be resumed. In addition, for loans we originate, the related origination expenses are deferred and recognized as a component of interest income, however expenses related to loans we acquire are included in general and administrative expenses as incurred. Cash, Cash Equivalents, and Restricted Cash Cash and cash equivalents represent cash held in banks and liquid investments with original maturities of three months or less. We may have bank balances in excess of federally insured amounts; however, we deposit our cash and cash equivalents with high credit-quality institutions to minimize credit risk exposure. We have not experienced, and do not expect, any losses on our cash or cash equivalents. Restricted cash represents cash held in a segregated bank account related to a letter of credit. The following table provides a reconciliation of cash, cash equivalents, and restricted cash in our consolidated balance sheets to the total amount shown in our consolidated statements of cash flows ($ in thousands): September 30, 2018 September 30, 2017 Cash and cash equivalents $ 86,987 $ 61,221 Restricted cash — 32,864 Total cash, cash equivalents, and restricted cash shown in our consolidated statements of cash flows $ 86,987 $ 94,085 Loans Receivable and Provision for Loan Losses We originate and purchase commercial real estate debt and related instruments generally to be held as long-term investments at amortized cost. We are required to periodically evaluate each of these loans for possible impairment. Impairment is indicated when it is deemed probable that we will not be able to collect all amounts due to us pursuant to the contractual terms of the loan. If a loan is determined to be impaired, we write down the loan through a charge to the provision for loan losses. Impairment of these loans, which are collateral dependent, is measured by comparing the estimated fair value of the underlying collateral, less costs to sell, to the book value of the respective loan. These valuations require significant judgments, which include assumptions regarding capitalization rates, leasing, creditworthiness of major tenants, occupancy rates, availability of financing, exit plan, loan sponsorship, actions of other lenders, and other factors deemed necessary by our Manager. Actual losses, if any, could ultimately differ from these estimates. Our Manager performs a quarterly review of our portfolio of loans. In conjunction with this review, our Manager assesses the risk factors of each loan, and assigns it a risk rating based on a variety of factors, including, without limitation, loan-to-value 5-point 1 - Very Low Risk 2 - Low Risk 3 - Medium Risk 4 - High Risk/Potential for Loss: 5 - Impaired/Loss Likely: During the second quarter of 2015, we acquired a portfolio of loans from General Electric Capital Corporation and certain of its affiliates, or the GE portfolio, for a total purchase price of $4.7 billion. We allocated the aggregate purchase price between each loan based on its fair value relative to the overall portfolio, which allocation resulted in purchase discounts or premiums determined on an asset-by-asset Debt Securities Held-to-Maturity We classify our debt securities as held-to-maturity, If, based on current information and events, there is an adverse change in cash flows expected to be collected from the cash flows previously projected for one of our debt securities, an other-than-temporary impairment is deemed to have occurred. A change in expected cash flows is considered adverse if the present value of the revised cash flows (taking into consideration both the timing and amount of cash flows expected to be collected), discounted using the debt security’s current yield, is less than the present value of the previously estimated remaining cash flows. If an other-than-temporary impairment is considered to have occurred, the debt security is written down to fair value. The total other-than-temporary impairment is bifurcated into (i) the amount related to expected credit losses, and (ii) the amount related to fair value adjustments in excess of expected credit losses. The other-than-temporary impairment related to expected credit losses is calculated by comparing the amortized cost basis of the security to the present value of cash flows expected to be collected, discounted at the security’s current yield, and is recognized in earnings in the consolidated statement of operations. The remaining other-than-temporary impairment that is not related to expected credit losses is recognized in other comprehensive income (loss). A portion of other-than-temporary impairments recognized through earnings is accreted back to the amortized cost basis of the security through interest income, while amounts recognized through other comprehensive income (loss) are amortized over the life of the security with no impact on earnings. Derivative Financial Instruments We classify all derivative financial instruments as either other assets or other liabilities on our consolidated balance sheets at fair value. On the date we enter into a derivative contract, we designate each contract as (i) a hedge of a net investment in a foreign operation, or net investment hedge, (ii) a hedge of a forecasted transaction or of the variability of cash flows to be received or paid related to a recognized asset or liability, or cash flow hedge, (iii) a hedge of a recognized asset or liability, or fair value hedge, or (iv) a derivative instrument not to be designated as a hedging derivative, or non-designated non-designated On a quarterly basis, we also formally assess whether the derivative we designated in each hedging relationship is expected to be, and has been, highly effective in offsetting changes in the value or cash flows of the hedged items. If it is determined that a derivative is not highly effective at hedging the designated exposure, hedge accounting is discontinued and the changes in fair value of the instrument are included in net income prospectively. Changes in the fair value of our derivative instruments that qualify as hedges are reported as a component of accumulated other comprehensive income (loss) on our consolidated financial statements. Deferred gains and losses are reclassified out of accumulated other comprehensive income (loss) and into net income in the same period or periods during which the hedged transaction affects earnings, and are presented in the same line item as the earnings effect of the hedged item. For cash flow hedges, this is typically when the periodic swap settlements are made, while for net investment hedges, this occurs when the hedged item is sold or substantially liquidated. To the extent a derivative does not qualify for hedge accounting and is deemed a non-designated Secured Debt Agreements Where applicable, we record investments financed with repurchase agreements as separate assets and the related borrowings under any repurchase agreements are recorded as separate liabilities on our consolidated balance sheets. Interest income earned on the investments and interest expense incurred on the repurchase agreements are reported separately on our consolidated statements of operations. Senior Loan Participations In certain instances, we finance our loans through the non-recourse non-consolidated Convertible Notes The “Debt with Conversion and Other Options” Topic of the Financial Accounting Standards Board, or FASB, Accounting Standards Codification, or ASC, requires the liability and equity components of convertible debt instruments that may be settled in cash upon conversion, including partial cash settlement, to be separately accounted for in a manner that reflects the issuer’s nonconvertible debt borrowing rate. The initial proceeds from the sale of convertible notes are allocated between a liability component and an equity component in a manner that reflects interest expense at the rate of similar nonconvertible debt that could have been issued at such time. The equity component represents the excess initial proceeds received over the fair value of the liability component of the notes as of the date of issuance. We measured the estimated fair value of the debt component of our convertible notes as of the respective issuance dates based on our nonconvertible debt borrowing rate. The equity component of each series of our convertible notes is reflected within additional paid-in non-cash non-cash Deferred Financing Costs The deferred financing costs that are included as a reduction in the net book value of the related liability on our consolidated balance sheets include issuance and other costs related to our debt obligations. These costs are amortized as interest expense using the effective interest method over the life of the related obligations. Fair Value of Financial Instruments The “Fair Value Measurements and Disclosures” Topic of the FASB, or ASC 820, defines fair value, establishes a framework for measuring fair value, and requires certain disclosures about fair value measurements under GAAP. Specifically, this guidance defines fair value based on exit price, or the price that would be received upon the sale of an asset or the transfer of a liability in an orderly transaction between market participants at the measurement date. ASC 820 also establishes a fair value hierarchy that prioritizes and ranks the level of market price observability used in measuring financial instruments. Market price observability is affected by a number of factors, including the type of financial instrument, the characteristics specific to the financial instrument, and the state of the marketplace, including the existence and transparency of transactions between market participants. Financial instruments with readily available quoted prices in active markets generally will have a higher degree of market price observability and a lesser degree of judgment used in measuring fair value. Financial instruments measured and reported at fair value are classified and disclosed based on the observability of inputs used in the determination, as follows: • Level 1: Generally includes only unadjusted quoted prices that are available in active markets for identical financial instruments as of the reporting date. • Level 2: Pricing inputs include quoted prices in active markets for similar instruments, quoted prices in less active or inactive markets for identical or similar instruments where multiple price quotes can be obtained, and other observable inputs, such as interest rates, yield curves, credit risks, and default rates. • Level 3: Pricing inputs are unobservable for the financial instruments and include situations where there is little, if any, market activity for the financial instrument. These inputs require significant judgment or estimation by management of third-parties when determining fair value and generally represent anything that does not meet the criteria of Levels 1 and 2. The estimated value of each asset reported at fair value using Level 3 inputs is determined by an internal committee composed of members of senior management of our Manager, including our Chief Executive Officer, Chief Financial Officer, and other senior officers. Certain of our other assets are reported at fair value either (i) on a recurring basis, as of each quarter-end, We are also required by GAAP to disclose fair value information about financial instruments, which are not otherwise reported at fair value in our consolidated balance sheet, to the extent it is practicable to estimate a fair value for those instruments. These disclosure requirements exclude certain financial instruments and all non-financial The following methods and assumptions are used to estimate the fair value of each class of financial instruments, for which it is practicable to estimate that value: • Cash and cash equivalents: The carrying amount of cash and cash equivalents approximates fair value. • Restricted cash: The carrying amount of restricted cash approximates fair value. • Loans receivable, net: The fair values of these loans were estimated by our Manager based on a discounted cash flow methodology, taking into consideration various factors including capitalization rates, discount rates, leasing, occupancy rates, availability and cost of financing, exit plan, sponsorship, actions of other lenders, and indications of market value from other market participants. • Debt securities held-to-maturity: • Derivative financial instruments: The fair value of our foreign currency and interest rate contracts was estimated using advice from a third-party derivative specialist, based on contractual cash flows and observable inputs comprising foreign currency rates and credit spreads. • Secured debt agreements, net: The fair value of these instruments was estimated based on the rate at which a similar credit facility would currently be priced. • Loan participations sold, net: The fair value of these instruments was estimated based on the value of the related loan receivable asset. • Securitized debt obligations, net: The fair value of these instruments was estimated by utilizing third-party pricing service providers. In determining the 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. • Convertible notes, net: Each series of the convertible notes is actively traded and their fair values were obtained using quoted market prices. Income Taxes Our financial results generally do not reflect provisions for current or deferred income taxes on our REIT taxable income. We believe that we operate in a manner that will continue to allow us to be taxed as a REIT and, as a result, we generally do not expect to pay substantial corporate level taxes other than those payable by our taxable REIT subsidiaries. If we were to fail to meet these requirements, we may be subject to federal, state, and local income tax on current and past income, and penalties. Refer to Note 12 for additional information. Stock-Based Compensation Our stock-based compensation consists of awards issued to our Manager and certain individuals employed by an affiliate of our Manager that vest over the life of the awards, as well as deferred stock units issued to certain members of our board of directors. Stock-based compensation expense is recognized for these awards in net income on a variable basis over the applicable vesting period of the awards, based on the value of our class A common stock. Refer to Note 13 for additional information. Earnings per Share Basic earnings per share, or Basic EPS, is computed in accordance with the two-class two-class Diluted earnings per share, or Diluted EPS, is determined using the treasury stock method, and is based on the net earnings allocable to our class A common stock, including restricted class A common stock and deferred stock units, divided by the weighted-average number of shares of our class A common stock, including restricted class A common stock and deferred stock units. Refer to Note 10 for additional discussion of earnings per share. Foreign Currency In the normal course of business, we enter into transactions not denominated in United States, or U.S., dollars. Foreign exchange gains and losses arising on such transactions are recorded as a gain or loss in our consolidated statements of operations. In addition, we consolidate entities that have a non-U.S. Non-U.S. non-U.S. Underwriting Commissions and Offering Costs Underwriting commissions and offering costs incurred in connection with common stock offerings are reflected as a reduction of additional paid-in Recent Accounting Pronouncements In June 2018, the FASB issued ASU 2018-07 2018-07. 2018-07 2018-07, 2018-07 2018-07 In June 2016, the FASB issued ASU 2016-13 “Financial ASU 2016-13. ASU 2016-13 significantly ASU 2016-13 will for available-for-sale debt ASU 2016-13 is ASU 2016-13 will In May 2014, the FASB issued ASU 2014-09, “Revenue , or ASU 2014-09. ASU 2014-09 broadly recognition. ASU 2014-09 is ASU 2014-09 in

Loans Receivable, Net

Loans Receivable, Net	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Loans Receivable, Net	3. LOANS RECEIVABLE, NET The following table details overall statistics for our loans receivable portfolio ($ in thousands): September 30, 2018 December 31, 2017 Number of loans 112 110 Principal balance $ 12,260,103 $ 10,108,226 Net book value $ 12,176,516 $ 10,056,732 Unfunded loan commitments (1) $ 3,046,350 $ 1,573,107 Weighted-average cash coupon (2) 5.61 % 5.55 % Weighted-average all-in (2) 5.94 % 5.95 % Weighted-average maximum maturity (years) (3) 3.8 3.5 (1) Unfunded commitments will primarily be funded to finance our borrowers’ construction or development of real estate-related assets, capital improvements of existing assets, or lease-related expenditures. These commitments will generally be funded over the term of each loan, subject in certain cases to an expiration date. (2) Our floating rate loans are indexed to various benchmark rates, with 83% and 92% of our floating rate loans by principal balance indexed to USD LIBOR as of September 30, 2018 and December 31, 2017, respectively. In addition to cash coupon, all-in all-in (3) Maximum maturity assumes all extension options are exercised by the borrower, however our loans may be repaid prior to such date. As of September 30, 2018, 86% of our loans by principal balance were subject to yield maintenance or other prepayment restrictions and 14% were open to repayment by the borrower without penalty. As of December 31, 2017, 75% of our loans were subject to yield maintenance or other prepayment restrictions and 25% were open to repayment by the borrower without penalty. Activity relating to our loans receivable portfolio was as follows ($ in thousands): Principal Balance Deferred Fees / Other Items (1) Net Book Value December 31, 2017 $ 10,108,226 $ (51,494 ) $ 10,056,732 Loan fundings 5,222,803 — 5,222,803 Loan repayments (2,452,811 ) — (2,452,811 ) Loan contributed to securitization (517,500 ) 5,498 (512,002 ) Unrealized (loss) gain on foreign currency translation (100,615 ) 678 (99,937 ) Deferred fees and other items — (74,111 ) (74,111 ) Amortization of fees and other items — 35,842 35,842 September 30, 2018 $ 12,260,103 $ (83,587 ) $ 12,176,516 (1) Other items primarily consist of purchase discounts or premiums, exit fees, and deferred origination expenses. The tables below detail the property type and geographic distribution of the properties securing the loans in our portfolio ($ in thousands): September 30, 2018 Property Type Number of Net Book Value Total Loan Exposure (1)(2) Percentage of Portfolio Office 49 $ 5,956,675 $ 6,006,534 47% Hotel 15 1,992,889 2,069,818 16 Multifamily 32 1,894,001 1,903,572 15 Spanish Assets 1 1,152,487 1,160,400 9 Retail 4 336,787 337,334 3 Condominium 2 84,429 158,462 1 Other 9 759,248 1,090,711 9 112 $ 12,176,516 $ 12,726,831 100% Geographic Location Number of Net Book Value Total Loan (1)(2) Percentage of United States Northeast 30 $ 3,796,633 $ 3,830,021 29% West 25 2,543,743 2,637,582 21 Southeast 18 2,025,381 2,034,852 16 Midwest 8 901,310 906,102 7 Southwest 13 477,809 480,792 4 Northwest 2 141,199 141,630 1 Subtotal 9,886,075 10,030,979 78 International Spain 1 1,152,487 1,160,400 9 United Kingdom 5 492,790 837,688 7 Canada 5 335,957 332,841 3 Australia 2 218,286 220,335 2 Belgium 1 71,494 71,945 1 Germany 1 11,814 65,000 — Netherlands 1 7,613 7,643 — Subtotal 16 2,290,441 2,695,852 22 Total 112 $ 12,176,516 $ 12,726,831 100% (1) In certain instances, we finance our loans through the non-recourse non-consolidated (2) Excludes investment exposure to the $1.0 billion 2018 Single Asset Securitization. See Note 4 for details of the subordinated risk retention interest we own in the 2018 Single Asset Securitization. December 31, 2017 Property Type Number of Net Book Value Total Loan (1) Percentage of Office 53 $ 5,773,972 $ 5,807,170 53% Hotel 15 1,830,568 1,905,497 17 Multifamily 25 1,220,423 1,228,959 11 Retail 6 487,473 940,980 8 Condominium 2 142,342 268,751 2 Other 9 601,954 942,251 9 110 $ 10,056,732 $ 11,093,608 100% Geographic Location Number of Net Book Value Total Loan (1) Percentage of United States Northeast 26 $ 2,857,948 $ 2,871,219 26% West 29 2,672,069 2,816,276 24 Southeast 17 2,007,202 2,470,992 22 Midwest 9 856,559 862,578 8 Southwest 10 380,204 380,120 3 Northwest 2 283,381 286,221 3 Subtotal 93 9,057,363 9,687,406 86 International United Kingdom 6 440,317 794,789 7 Canada 7 415,893 412,343 4 Belgium 1 73,779 74,431 1 Germany 1 12,237 67,399 1 Netherlands 2 57,143 57,240 1 Subtotal 17 999,369 1,406,202 14 Total 110 $ 10,056,732 $ 11,093,608 100% (1) In certain instances, we finance our loans through the non-recourse non-consolidated Loan Risk Ratings As further described in Note 2, our Manager evaluates our loan portfolio on a quarterly basis. In conjunction with our quarterly loan portfolio review, our Manager assesses the risk factors of each loan, and assigns a risk rating based on several factors. Factors considered in the assessment include, but are not limited to, risk of loss, current LTV, debt yield, collateral performance, structure, exit plan, and sponsorship. Loans are rated “1” (less risk) through “5” (greater risk), which ratings are defined in Note 2. The following table allocates the principal balance and net book value of our loans receivable based on our internal risk ratings ($ in thousands): September 30, 2018 December 31, 2017 Risk Rating Number of Loans Net Book Value Total Loan Exposure (1)(2) Risk Rating Number of Loans Net Book Value Total Loan Exposure (1) 1 1 $ 53,849 $ 53,873 1 1 $ 31,842 $ 31,890 2 43 4,167,871 4,272,068 2 41 3,512,709 3,521,701 3 68 7,954,796 8,400,890 3 67 6,491,617 7,519,465 4 — — — 4 1 20,564 20,552 5 — — — 5 — — — 112 $ 12,176,516 $ 12,726,831 110 $ 10,056,732 $ 11,093,608 (1) In certain instances, we finance our loans through the non-recourse non-consolidated (2) Excludes investment exposure to the $1.0 billion 2018 Single Asset Securitization. See Note 4 for details of the subordinated risk retention interest we own in the 2018 Single Asset Securitization. The weighted-average risk rating of our total loan exposure was 2.7 as of both September 30, 2018 and December 31, 2017. We had one loan with a risk rating of “4” in our portfolio as of December 31, 2017, which was repaid in full in April 2018. We did not have any impaired loans, nonaccrual loans, or loans in maturity default as of September 30, 2018 or December 31, 2017. Multifamily Joint Venture As discussed in Note 2, we entered into a Multifamily Joint Venture in April 2017. As of September 30, 2018 and December 31, 2017, our Multifamily Joint Venture held $222.7 million and $182.2 million of loans, respectively, which are included in the loan disclosures above. Refer to Note 2 for additional discussion of our Multifamily Joint Venture.

Other Assets and Liabilities

Other Assets and Liabilities	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Other Assets and Liabilities	4. OTHER ASSETS AND LIABILITIES The following table details the components of our other assets ($ in thousands): September 30, 2018 December 31, 2017 Debt securities held-to-maturity (1) $ 96,050 $ — Accrued interest receivable 45,762 38,573 Collateral deposited under derivative agreements 7,360 4,120 Loan portfolio payments held by servicer (2) 3,902 54,759 Derivative assets 2,719 1,214 Prepaid expenses 151 798 Prepaid taxes 28 31 Other — 80 Total $ 155,972 $ 99,575 (1) Represents a $99.0 million subordinate risk retention interest in the $1.0 billion 2018 Single Asset Securitization, with a yield to full maturity of L+10.0% and a maximum maturity date of June 9, 2025, assuming all extension options are exercised by the borrower. Refer to Note 15 for additional discussion. (2) Represents loan principal and interest payments held by our third-party loan servicer as of the balance sheet date which were remitted to us during the subsequent remittance cycle. The following table details the components of our other liabilities ($ in thousands): September 30, 2018 December 31, 2017 Accrued dividends payable $ 74,195 $ 66,888 Accrued interest payable 23,701 14,162 Accrued management and incentive fees payable 18,368 14,284 Derivative liabilities 3,676 4,911 Accounts payable and other liabilities 3,426 2,125 Secured debt repayments pending servicer remittance (1) — 38,456 Total $ 123,366 $ 140,826 (1) Represents pending transfers from our third-party loan servicer that were remitted to our banking counterparties during the subsequent remittance cycle.

Secured Debt Agreements, Net

Secured Debt Agreements, Net	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Secured Debt Agreements, Net	5. SECURED DEBT AGREEMENTS, NET Our secured debt agreements include credit facilities, the GE portfolio acquisition facility, asset-specific financings, and a revolving credit agreement. The following table details our secured debt agreements ($ in thousands): Secured Debt Agreements Borrowings Outstanding September 30, 2018 December 31, 2017 Credit facilities $ 4,850,911 $ 4,068,249 Asset-specific financings 1,499,286 518,864 GE portfolio acquisition facility 512,059 703,423 Revolving credit agreement — — Total secured debt agreements $ 6,862,256 $ 5,290,536 Deferred financing costs (1) (20,497 ) (16,681 ) Net book value of secured debt $ 6,841,759 $ 5,273,855 (1) Costs incurred in connection with our secured debt agreements are recorded on our consolidated balance sheet when incurred and recognized as a component of interest expense over the life of each related agreement. Credit Facilities During the nine months ended September 30, 2018, we added one new credit facility, providing an additional $1.0 billion of credit capacity, and increased the maximum facility size of one of our existing credit facilities, providing an additional $250.0 million of credit capacity. The following tables detail our credit facilities ($ in thousands): September 30, 2018 Maximum Credit Borrowings Collateral Lender Facility Size (1) Potential (2) Outstanding Available (2) Assets (3) Bank of America $ 1,000,000 $ 863,592 $ 863,592 $ — $ 1,091,860 Wells Fargo 2,000,000 1,160,678 850,687 309,991 1,577,251 MetLife 1,000,000 737,770 737,770 — 946,933 Barclays 1,000,000 617,360 617,360 — 771,700 Citibank (4) 750,000 576,369 480,129 96,240 730,723 JP Morgan 500,000 435,095 332,909 102,186 564,070 Morgan Stanley (5) 651,550 329,256 278,770 50,486 461,760 Deutsche Bank 500,000 277,247 277,247 — 380,986 Société Générale (6) 464,160 235,229 235,229 — 298,951 Goldman Sachs - Multi. JV (7) 250,000 117,498 117,498 — 148,099 Bank of America - Multi. JV (7) 200,000 59,720 59,720 — 74,650 $ 8,315,710 $ 5,409,814 $ 4,850,911 $ 558,903 $ 7,046,983 December 31, 2017 Maximum Credit Borrowings Collateral Lender Facility Size (1) Potential (2) Outstanding Available (2) Assets (3) Wells Fargo $ 2,000,000 $ 1,289,135 $ 1,170,801 $ 118,334 $ 1,680,325 MetLife 1,000,000 807,164 807,164 — 1,039,231 Bank of America 750,000 573,542 573,542 — 765,049 JP Morgan 500,000 443,496 319,755 123,741 579,218 Société Générale (6) 480,200 300,871 300,871 — 373,181 Deutsche Bank 500,000 295,743 295,743 — 399,203 Citibank (4) 800,125 354,354 240,881 113,473 455,433 Morgan Stanley (5) 675,650 456,344 216,044 240,300 591,168 Bank of America - Multi. JV (7) 200,000 85,560 85,560 — 106,950 Goldman Sachs - Multi. JV (7) 250,000 57,888 57,888 — 75,225 $ 7,155,975 $ 4,664,097 $ 4,068,249 $ 595,848 $ 6,064,983 (1) Maximum facility size represents the largest amount of borrowings available under a given facility once sufficient collateral assets have been approved by the lender and pledged by us. (2) Potential borrowings represents the total amount we could draw under each facility based on collateral already approved and pledged. When undrawn, these amounts are immediately available to us at our sole discretion under the terms of each credit facility. (3) Represents the principal balance of the collateral assets. (4) As of September 30, 2018, the Citibank facility was denominated in U.S. dollars. As of December 31, 2017, the maximum facility size was composed of a $500.0 million facility denominated in U.S. dollars plus a €250.0 million facility, which translated to $300.1 million as of such date. (5) As of September 30, 2018 and December 31, 2017, the Morgan Stanley maximum facility size was £500.0 million, which translated to $651.6 million and $675.7 million, respectively. (6) As of September 30, 2018 and December 31, 2017, the Société Générale maximum facility size was €400.0 million, which translated to $464.2 million and $480.2 million, respectively. (7) These facilities finance the loan investments of our consolidated Multifamily Joint Venture. Refer to Note 2 for additional discussion of our Multifamily Joint Venture. The weighted-average outstanding balance of our credit facilities was $4.4 billion for the nine months ended September 30, 2018. As of September 30, 2018, we had aggregate borrowings of $4.9 billion outstanding under our credit facilities, with a weighted-average cash coupon of LIBOR plus 1.77% per annum, a weighted-average all-in term-out The weighted-average outstanding balance of our credit facilities was $4.2 billion for the nine months ended December 31, 2017. As of December 31, 2017, we had aggregated borrowings of $4.1 billion outstanding under our credit facilities, with a weighted-average cash coupon of LIBOR plus 1.90% per annum, a weighted-average all-in term-out Borrowings under each facility are subject to the initial approval of eligible collateral loans by the lender and the maximum advance rate and pricing rate of individual advances are determined with reference to the attributes of the respective collateral loan. The following tables outline the key terms of our credit facilities as of September 30, 2018: Lender Currency Guarantee (1) Margin Call (2) Term/Maturity Morgan Stanley $ / £ / € 25% Collateral marks only March 3, 2020 Goldman Sachs - Multi. JV (3) $ 25% Collateral marks only July 12, 2020 (4) JP Morgan $ / £ 50% Collateral marks only January 7, 2021 Bank of America - Multi. JV (3) $ 43% Collateral marks only July 19, 2021 (5) Deutsche Bank $ 32% Collateral marks only August 9, 2021 (6) Barclays $ 25% Collateral marks only March 29, 2023 (7) MetLife $ 50% Collateral marks only April 22, 2023 (8) Bank of America $ 50% Collateral marks only May 21, 2023 (9) Citibank $ / £ / € 25% Collateral marks only Term matched (10) Société Générale $ / £ / € 25% Collateral marks only Term matched (10) Wells Fargo $ 25% Collateral marks only Term matched (10) (1) Other than amounts guaranteed based on specific collateral asset types, borrowings under our credit facilities are non-recourse (2) Margin call provisions under our credit facilities do not permit valuation adjustments based on capital markets events, and are limited to collateral-specific credit marks. (3) These facilities finance the loan investments of our consolidated Multifamily Joint Venture. Refer to Note 2 for additional discussion of our Multifamily Joint Venture. (4) Includes a one-year (5) Includes two one-year (6) Includes two one-year (7) Includes four one-year (8) Includes four one-year (9) Includes two one-year (10) These credit facilities have various availability periods during which new advances can be made and which are generally subject to each lender’s discretion. Maturity dates for advances outstanding are tied to the term of each respective collateral asset. Currency Potential Outstanding Borrowings (1) Floating Rate Index Spread (2) Advance Rate (3) $ $ 5,024,025 $ 4,551,603 1-month 1.75% 79.2% € € 54,869 € 12,100 3-month 2.28% 80.0% £ £ 247,194 £ 218,914 3-month 1.97% 79.0% $ 5,409,815 $ 4,850,911 1.77% 79.2% (1) Potential borrowings represents the total amount we could draw under each facility based on collateral already approved and pledged. When undrawn, these amounts are immediately available to us at our sole discretion under the terms of each credit facility. (2) Represents weighted-average spread over the applicable floating rate index, based on borrowings outstanding. (3) Represents weighted-average advance rate based on the approved outstanding principal balance of the collateral assets pledged. Asset-Specific Financings During the nine months ended September 30, 2018, we entered into an €800.0 million asset-specific September 30, 2018 Asset-Specific Financings Count Principal Book Value Wtd. Avg. (1) Guarantee (2) Wtd. Avg. (3) Collateral assets 5 $ 1,905,475 $ 1,895,094 L+3.61 % n/a Sep. 2022 Financing provided (4) 5 $ 1,499,286 $ 1,492,614 L+1.77 % $ 1,178,874 Sep. 2022 December 31, 2017 Asset-Specific Financings Count Principal Book Value Wtd. Avg. (1) Guarantee (2) Wtd. Avg. (3) Collateral assets 6 $ 682,259 $ 677,296 L+4.76 % n/a Dec. 2020 Financing provided (4) 6 $ 518,864 $ 517,088 L+2.50 % $ 162,475 Dec. 2020 (1) These floating rate loans and related liabilities are indexed to the various benchmark rates relevant in each arrangement in terms of currency and payment frequency. Therefore the net exposure to each benchmark rate is in direct proportion to our net assets indexed to that rate. In addition to cash coupon, yield/cost includes the amortization of deferred origination fees / financing costs. (2) Other than amounts guaranteed on an asset-by-asset basis, borrowings under our asset-specific financings are non-recourse to us. (3) The weighted-average term is determined based on the maximum maturity of the corresponding loans, assuming all extension options are exercised by the borrower. Each of our asset-specific financings are term-matched to the corresponding collateral loans. (4) As of September 30, 2018 and December 31, 2017, borrowings of $517.8 million and $394.8 million, respectively, under these asset specific financings are cross collateralized with related credit facilities with the same lenders. The weighted-average outstanding balance of our asset-specific financings was $1.3 billion for the nine months ended September 30, 2018 and $522.5 million for the nine months ended December 31, 2017. GE Portfolio Acquisition Facility During the second quarter of 2015, concurrently with our acquisition of the GE portfolio, we entered into an agreement with Wells Fargo to provide us with secured financing for the acquired portfolio. The GE portfolio acquisition facility is non-revolving September 30, 2018 GE Portfolio Acquisition Facility Count Principal (1) Book Value Wtd. Avg. (2) Guarantee (3) Wtd. Avg. (4) Collateral assets 11 $ 662,464 $ 664,189 5.92 % n/a May 2021 Financing provided 11 $ 512,059 $ 511,346 L+1.77 % $ 250,000 May 2021 December 31, 2017 GE Portfolio Acquisition Facility Count Principal (1) Book Value Wtd. Avg. (2) Guarantee (3) Wtd. Avg. (4) Collateral assets 16 $ 906,707 $ 911,092 5.74 % n/a Jul. 2020 Financing provided 16 $ 703,423 $ 702,337 L+1.72 % $ 250,000 Jul. 2020 (1) As of September 30, 2018, this facility provided for $608.7 million of financing, of which $512.1 million was outstanding and an additional $96.6 million was available to finance future loan fundings in the GE portfolio. As of December 31, 2017, this facility provided for $816.3 million of financing, of which $703.4 million was outstanding and an additional $112.9 million was available to finance future loan fundings in the GE portfolio. (2) In addition to cash coupon, yield/cost includes the amortization of deferred origination fees / financing costs. (3) We guarantee obligations under the GE portfolio acquisition facility in an amount equal to the greater of (i) 25% of outstanding asset-specific borrowings, and (ii) $250.0 million. (4) The weighted-average term is determined based on the maximum maturity of the corresponding loans, assuming all extension options are exercised by the borrower. Each of our asset-specific financings are term-matched to the corresponding collateral loans. Revolving Credit Agreement We have a $250.0 million full recourse secured revolving credit agreement with Barclays that is designed to finance first mortgage originations for up to six months as a bridge to term financing or syndication. Advances under the agreement are subject to availability under a specified borrowing base and accrue interest at a per annum pricing rate equal to the sum of (i) an applicable base rate or Eurodollar rate and (ii) an applicable margin, in each case, dependent on the applicable type of loan collateral. The maturity date of the facility is April 4, 2020. During the nine months ended September 30, 2018, the weighted-average outstanding borrowings under the revolving credit agreement was $37.8 million and we recorded interest expense of $2.6 million, including $825,000 of amortization of deferred fees and expenses. As of September 30, 2018, we had no outstanding borrowings under the agreement. During the nine months ended December 31, 2017, the weighted-average outstanding borrowings under the revolving credit agreement was $40.7 million and we recorded interest expense of $2.6 million, including $703,000 of amortization of deferred fees and expenses. As of December 31, 2017, we had no outstanding borrowings under the agreement. Debt Covenants Each of the guarantees related to our secured debt agreements contain the following uniform financial covenants: (i) our ratio of earnings before interest, taxes, depreciation, and amortization, or EBITDA, to fixed charges, as defined in the agreements, shall be not less than 1.4 to 1.0; (ii) our tangible net worth, as defined in the agreements, shall not be less than $2.4 billion as of each measurement date plus 75% of the net cash proceeds of future equity issuances subsequent to September 30, 2018; (iii) cash liquidity shall not be less than the greater of (x) $10.0 million or (y) 5% of our recourse indebtedness; and (iv) our indebtedness shall not exceed 83.33% of our total assets. As of September 30, 2018 and December 31, 2017, we were in compliance with these covenants.

Loan Participations Sold, Net

Loan Participations Sold, Net	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Loan Participations Sold, Net	6. LOAN PARTICIPATIONS SOLD, NET The financing of a loan by the non-recourse The following tables detail our loan participations sold ($ in thousands): September 30, 2018 Loan Participations Sold Count Principal Book Value Yield/Cost (1) Guarantee (2) Term Total loan 1 $ 106,259 $ 105,149 L+6.06 % n/a Feb. 2022 Senior participation (3)(4) 1 81,170 81,044 L+4.08 % n/a Feb. 2022 December 31, 2017 Loan Participations Sold Count Principal Book Value Yield/Cost (1) Guarantee (2) Term Total loan 1 $ 141,119 $ 138,907 L+5.94 % n/a Feb. 2022 Senior participation (3)(4) 1 80,706 80,415 L+4.14 % n/a Feb. 2022 (1) Our floating rate loans and related liabilities are indexed to the various benchmark rates relevant in each arrangement in terms of currency and payment frequency. Therefore the net exposure to each benchmark rate is in direct proportion to our net assets indexed to that rate. In addition to cash coupon, yield/cost includes the amortization of deferred fees / financing costs. (2) As of September 30, 2018 and December 31, 2017, our loan participations sold was non-recourse to us. (3) During the three and nine months ended September 30, 2018, we recorded $11.7 million and $15.2 million, respectively, of interest expense related to our loan participations sold. During the three and nine months ended September 30, 2017, we recorded $4.0 million and $9.3 million, respectively, of interest expense related to our loan participations sold. (4) The difference between principal balance and book value of loan participations sold is due to deferred financing costs of $126,000 and $291,000, as of September 30, 2018 and December 31, 2017, respectively.

Securitized Debt Obligations, N

Securitized Debt Obligations, Net	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Securitized Debt Obligations, Net	7. SECURITIZED DEBT OBLIGATIONS, NET We have financed a pool of our loans through a collateralized loan obligation, or the CLO, and have also financed one of our loans through a single asset securitization vehicle, or the 2017 Single Asset Securitization. The CLO and the 2017 Single Asset Securitization have issued securitized debt obligations that are non-recourse The following tables detail our securitized debt obligations ($ in thousands): September 30, 2018 Securitized Debt Obligations Count Principal Book Value Wtd. Avg. Yield/Cost (1) Term (2) Collateralized Loan Obligation Collateral assets 28 $ 1,000,000 $ 1,000,000 6.09 % Feb. 2022 Financing provided 1 817,500 809,944 L+1.74 % June 2035 2017 Single Asset Securitization Collateral assets (3) 1 678,963 675,437 L+3.60 % June 2023 Financing provided 1 474,620 474,418 L+1.65 % June 2033 Total Collateral assets 29 $ 1,678,963 $ 1,675,437 6.00 % Financing provided (4) 2 $ 1,292,120 $ 1,284,362 L+1.71 % December 31, 2017 Securitized Debt Obligations Count Principal Book Value Wtd. Avg. Yield/Cost (1) Term (2) Collateralized Loan Obligation Collateral assets 31 $ 1,000,000 $ 1,000,000 5.16 % Nov. 2021 Financing provided 1 817,500 808,083 L+1.76 % June 2035 2017 Single Asset Securitization Collateral assets (3) 1 656,406 652,880 L+3.60 % June 2023 Financing provided 1 474,620 474,328 L+1.94 % June 2033 Total Collateral assets 32 $ 1,656,406 $ 1,652,880 5.17 % Financing provided (4) 2 $ 1,292,120 $ 1,282,411 L+1.83 % (1) As of September 30, 2018, 98% of our loans financed by securitized debt obligations earned a floating rate of interest. As of December 31, 2017, 98% of our loans financed by securitized debt obligations earned a floating rate of interest. In addition to cash coupon, all-in All-in (2) Loan term represents weighted-average final maturity, assuming all extension options are exercised by the borrower. Repayments of securitized debt obligations are tied to timing of the related collateral loan asset repayments. The term of these obligations represents the rated final distribution date of the securitizations. (3) The collateral assets for the 2017 Single Asset Securitization include the total loan amount, of which we securitized $500.0 million. (4) During the three and nine months ended September 30, 2018, we recorded $12.5 million and $35.6 million of interest expense, respectively, related to our securitized debt obligations. During both the three and nine months ended September 30, 2017, we recorded $3.8 million of interest expense related to our securitized debt obligations.

Convertible Notes, Net

Convertible Notes, Net	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Convertible Notes, Net	8. CONVERTIBLE NOTES, NET As of September 30, 2018, the following convertible senior notes, or Convertible Notes, were outstanding ($ in thousands): Convertible Notes Issuance Face Value Coupon Rate All-in Cost (1) Conversion Rate (2) Maturity November 2013 $ 172,328 5.25 % 5.87 % 36.5472 December 1, 2018 May 2017 402,500 4.38 % 4.85 % 28.0324 May 5, 2022 March 2018 220,000 4.75 % 5.33 % 27.6052 March 15, 2023 (1) Includes issuance costs that are amortized through interest expense over the life of the Convertible Notes using the effective interest method. (2) Represents the shares of class A common stock per $1,000 principal amount of Convertible Notes, which is equivalent to a conversion price of $27.36, $35.67, and $36.23 per share of class A common stock, respectively, for the November 2013, May 2017, and March 2018 convertible notes. As a result of exceeding the cumulative dividend threshold, as defined in the November 2013 convertible notes supplemental indenture, the conversion rate on the November 2013 convertible notes was most recently adjusted on March 28, 2018 from the prior conversion rate of 36.1380 shares of class A common stock per $1,000 principal amount of convertible notes, which was equivalent to a conversion price of $27.67 per share of class A common stock. Pursuant to the terms of the November 2013 supplemental indenture, the conversion rate will be adjusted to 36.8161 on the first day of any future observation period related to a conversion of the November 2013 convertible notes to account for the dividends paid on our class A common stock on July 16, 2018 and October 15, 2018. The cumulative dividend threshold as defined in the respective May 2017 and March 2018 convertible notes supplemental indentures have not been exceeded as of September 30, 2018. The Convertible Notes are convertible at the holders’ option into shares of our class A common stock, only under specific circumstances, prior to the close of business on August 31, 2018, January 31, 2022, and December 14, 2022 for the November 2013, May 2017, and March 2018 convertible notes, respectively, at the applicable conversion rate in effect on the conversion date. Thereafter, the Convertible Notes are convertible at the option of the holder at any time until the second scheduled trading day immediately preceding the maturity date. We may not redeem the Convertible Notes prior to maturity. The last reported sale price of our class A common stock of $33.51 on September 28, 2018, the last trading day in the quarter ended September 30, 2018, was greater than the per share conversion price of the November 2013 convertible notes but less than the per share conversion price of the May 2017 and March 2018 convertible notes. We have the intent and ability to settle each series of the Convertible Notes in cash and, as a result, the Convertible Notes did not have any impact on our diluted earnings per share. During the nine months ended September 30, 2018, holders of $172,000 of our November 2013 convertible notes elected to convert their notes pursuant to the terms of the November 2013 convertible notes supplemental indenture. The conversions were settled entirely in cash. Upon our issuance of the November 2013 convertible notes, we recorded a $9.1 million discount based on the implied value of the conversion option and an assumed effective interest rate of 6.50%, as well as $4.1 million of initial issuance costs. Including the amortization of this discount and the issuance costs, our total cost of the November 2013 convertible notes issuance is 7.16% per annum. Upon our issuance of the May 2017 convertible notes, we recorded a $979,000 discount based on the implied value of the conversion option and an assumed effective interest rate of 4.57%, as well as $8.4 million of initial debt discount and issuance costs. Including the amortization of the discount and issuance costs, our total cost of the May 2017 convertible notes issuance is 4.91% per annum. Upon our issuance of the March 2018 convertible notes, we recorded a $1.5 million discount based on the implied value of the conversion option and an assumed effective interest rate of 5.25%, as well as $5.2 million of initial debt discount and issuance costs. Including the amortization of the discount and issuance costs, our total cost of the March 2018 convertible notes issuance is 5.49% per annum. The following table details the net book value of our Convertible Notes on our consolidated balance sheets ($ in thousands): September 30, 2018 Face value $ 794,828 $ 575,000 Unamortized discount (12,956 ) (10,279 ) Deferred financing costs (921 ) (810 ) Net book value $ 780,951 $ 563,911 The following table details our interest expense related to the Convertible Notes ($ in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Cash coupon $ 9,277 $ 6,247 $ 25,333 $ 12,732 Discount and issuance cost amortization 1,535 1,202 4,242 2,869 Total interest expense $ 10,812 $ 7,449 $ 29,575 $ 15,601 Accrued interest payable for the Convertible Notes was $10.8 million and $3.7 million as of September 30, 2018, and December 31, 2017, respectively. Refer to Note 2 for additional discussion of our accounting policies for the Convertible Notes.

Derivative Financial Instrument

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	9. DERIVATIVE FINANCIAL INSTRUMENTS The sole objective of our use of derivative financial instruments is to minimize the risks and/or costs associated with our investments and/or financing transactions. These derivatives may or may not qualify as net investment, cash flow, or fair value hedges under the hedge accounting requirements of ASC 815 – “Derivatives and Hedging.” Derivatives not designated as hedges are not speculative and are used to manage our exposure to interest rate movements and other identified risks. For more information on the accounting for designated and non-designated The use of derivative financial instruments involves certain risks, including the risk that the counterparties to these contractual arrangements do not perform as agreed. To mitigate this risk, we only enter into derivative financial instruments with counterparties that have appropriate credit ratings and are major financial institutions with which we and our affiliates may also have other financial relationships. We do not anticipate that any of the counterparties will fail to meet their obligations. Net Investment Hedges of Foreign Currency Risk Certain of our international investments expose us to fluctuations in foreign interest rates and currency exchange rates. These fluctuations may impact the value of our cash receipts and payments in terms of our functional currency, the U.S. dollar. We use foreign currency forward contracts to protect the value or fix the amount of certain investments or cash flows in terms of the U.S. dollar. The following table details our outstanding foreign exchange derivatives that were designated as net investment hedges of foreign currency risk (notional amount in thousands): September 30, 2018 December 31, 2017 Foreign Currency Derivatives Number of Notional Amount Foreign Currency Derivatives Number of Notional Amount Sell AUD Forward 3 A$ 305,000 Sell GBP Forward 1 £ 112,700 Sell EUR Forward 1 € 185,000 Sell CAD Forward 1 C$ 95,100 Sell GBP Forward 1 £ 79,100 Sell CAD Forward 1 C$ 71,600 Cash Flow Hedges of Interest Rate Risk Certain of our financing transactions expose us to a fixed versus floating rate mismatch between our assets and liabilities. We use derivative financial instruments, which include interest rate caps and swaps, and may also include interest rate options, floors, and other interest rate derivative contracts, to hedge interest rate risk associated with our borrowings where there is potential for an index mismatch. The following tables detail our outstanding interest rate derivatives that were designated as cash flow hedges of interest rate risk (notional amount in thousands): September 30, 2018 Interest Rate Number of Notional Amount Strike Index Wtd.-Avg. Interest Rate Swaps 4 C$ 107,822 1.0% CDOR 0.7 Interest Rate Caps 9 $ 204,248 2.4% USD LIBOR 0.7 Interest Rate Caps 3 C$ 22,765 2.0% CDOR 0.4 December 31, 2017 Interest Rate Number of Notional Amount Strike Index Wtd.-Avg. Interest Rate Swaps 4 C$ 108,094 1.0% CDOR 1.4 Interest Rate Caps 9 $ 204,248 2.4% USD LIBOR 1.5 Interest Rate Caps 3 C$ 23,370 2.0% CDOR 0.3 Amounts reported in accumulated other comprehensive income (loss) related to derivatives will be reclassified to interest expense as interest payments are made on our floating rate debt. During the twelve months following September 30, 2018, we estimate that an additional $570,000 will be reclassified from accumulated other comprehensive income (loss) as an increase to interest income. Non-designated During the three and nine months ended September 30, 2018, we recorded losses of $51,000 and gains of $94,000, respectively, related to non-designated The following tables summarize our non-designated September 30, 2018 Non-designated Number of Notional Amount Buy GBP / Sell EUR Forward 1 € 12,857 December 31, 2017 Non-designated Number of Notional Buy GBP / Sell EUR Forward 1 € 12,857 Valuation of Derivative Instruments The following table summarizes the fair value of our derivative financial instruments ($ in thousands): Fair Value of Derivatives in an Asset Position (1) Fair Value of Derivatives in a Liability Position (2) September 30, 2018 September 30, 2018 Derivatives designated as hedging instruments: Foreign exchange contracts $ 1,514 $ — $ 3,676 $ 4,872 Interest rate derivatives 1,042 1,214 — — Total $ 2,556 $ 1,214 $ 3,676 $ 4,872 Derivatives not designated as hedging instruments: Foreign exchange contracts $ 163 $ — $ — $ 39 Interest rate derivatives — — — — Total $ 163 $ — $ — $ 39 Total Derivatives $ 2,719 $ 1,214 $ 3,676 $ 4,911 (1) Included in other assets in our consolidated balance sheets. (2) Included in other liabilities in our consolidated balance sheets. The following table presents the effect of our derivative financial instruments on our consolidated statements of operations ($ in thousands): Amount of Gain (Loss) Recognized in OCI on Derivatives Location of Amount of Gain (Loss) Reclassified from Accumulated OCI into Income Derivatives in Hedging Relationships Three Months Nine Months Gain (Loss) OCI into Income Three Months Nine Months Net Investment Hedges Foreign exchange contracts (1) $ 1,763 $ 23,782 Interest Expense $ — $ — Cash Flow Hedges Interest rate derivatives 92 228 Interest Expense (2) 152 388 Total $ 1,855 $ 24,011 $ 152 $ 388 (1) During the three and nine months ended September 30, 2018, we received net cash settlements of $7.6 million and $21.0 million, respectively, on our foreign currency forward contracts. Those amounts are included as a component of accumulated other comprehensive loss on our consolidated balance sheets. (2) During the three months ended September 30, 2018, we recorded total interest and related expenses of $98.0 million, which included a $152,000 expense reduction related to income generated by our cash flow hedges. During the nine months ended September 30, 2018, we recorded total interest and related expenses of $255.7 million, which included a $388,000 expense reduction related to income generated by our cash flow hedges. Credit-Risk Related Contingent Features We have entered into agreements with certain of our derivative counterparties that contain provisions where if we were to default on any of our indebtedness, including default where repayment of the indebtedness has not been accelerated by the lender, we may also be declared in default on our derivative obligations. In addition, certain of our agreements with our derivative counterparties require that we post collateral to secure net liability positions. As of September 30, 2018, we were in a net asset position with one of our derivative counterparties and in a net liability position with our other derivative counterparty, and posted collateral of $7.4 million under these derivative contracts. As of December 31, 2017, we were in a net asset position with one of our derivative counterparties and in a net liability position with our other derivative counterparty, and posted collateral of $4.1 million under these derivative contracts.

Equity

Equity	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Equity	10. EQUITY Stock and Stock Equivalents Authorized Capital As of September 30, 2018, we had the authority to issue up to 300,000,000 shares of stock, consisting of 200,000,000 shares of class A common stock and 100,000,000 shares of preferred stock. Subject to applicable NYSE listing requirements, our board of directors is authorized to cause us to issue additional shares of authorized stock without stockholder approval. In addition, to the extent not issued, currently authorized stock may be reclassified between class A common stock and preferred stock. We did not have any shares of preferred stock issued and outstanding as of September 30, 2018. Class A Common Stock and Deferred Stock Units Holders of shares of our class A common stock are entitled to vote on all matters submitted to a vote of stockholders and are entitled to receive such dividends as may be authorized by our board of directors and declared by us, in all cases subject to the rights of the holders of shares of outstanding preferred stock, if any. The following table details our issuance of class A common stock during the nine months ended September 30, 2018 ($ in thousands, except share and per share data): Class A Common Stock Offerings 2018 Total / August 2018 At-the-Market 2018 (1) Shares issued 6,900,000 4,583,135 11,483,135 Share issue price (2) $ 32.60 $ 32.73 $ 32.65 Net proceeds (3) $ 222,275 $ 147,512 $ 369,787 (1) Issuance represents shares issued under our at-the-market (2) Represents price per share paid by the underwriters or sales agents, as applicable. Net proceeds after underwriting or sales discounts and commissions were $32.26 and $32.24 per share for our August offering and at-the-market (3) Net proceeds represents proceeds received from the underwriters less applicable transaction costs. We also issue restricted class A common stock under our stock-based incentive plans. Refer to Note 13 for additional discussion of these long-term incentive plans. In addition to our class A common stock, we also issue deferred stock units to certain members of our board of directors in lieu of cash compensation for services rendered. These deferred stock units are non-voting, The following table details the movement in our outstanding shares of class A common stock, including restricted class A common stock and deferred stock units: Nine Months Ended September 30, Common Stock Outstanding (1) 2018 2017 Beginning balance 108,081,077 94,709,290 Issuance of class A common stock (2) 11,484,414 971 Issuance of restricted class A common stock, net 300,921 286,773 Issuance of deferred stock units 23,730 20,560 Ending balance 119,890,142 95,017,594 (1) Includes deferred stock units held by members of our board of directors of 220,947 and 189,587 as of September 30, 2018 and 2017, respectively. (2) Includes 1,279 and 971 shares issued under our dividend reinvestment program during the nine months ended September 30, 2018 and 2017, respectively. Dividend Reinvestment and Direct Stock Purchase Plan On March 25, 2014, we adopted a dividend reinvestment and direct stock purchase plan, under which we registered and reserved for issuance, in the aggregate, 10,000,000 shares of class A common stock. Under the dividend reinvestment component of this plan, our class A common stockholders can designate all or a portion of their cash dividends to be reinvested in additional shares of class A common stock. The direct stock purchase component allows stockholders and new investors, subject to our approval, to purchase shares of class A common stock directly from us. During the three and nine months ended September 30, 2018, we issued 403 shares and 1,279 shares, respectively, of class A common stock under the dividend reinvestment component of the plan compared to 428 shares and 971 shares for the same periods in 2017. As of September 30, 2018, a total of 9,995,647 shares of class A common stock remained available for issuance under the dividend reinvestment and direct stock purchase plan. At the Market Stock Offering Program On May 9, 2014, we entered into equity distribution agreements, or ATM Agreements, pursuant to which we may sell, from time to time, up to an aggregate sales price of $200.0 million of our class A common stock. On July 29, 2016, in connection with filing a new universal shelf registration statement on Form S-3, we Dividends We generally intend to distribute substantially all of our taxable income, which does not necessarily equal net income as calculated in accordance with GAAP, to our stockholders each year to comply with the REIT provisions of the Internal Revenue Code of 1986, as amended, or the Internal Revenue Code. Our On September 14, 2018, we declared a dividend of $0.62 per share, or $74.2 million, that was paid on October 15, 2018, to stockholders of record as of September 28, 2018. The following table details our dividend activity ($ in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Dividends declared per share of common stock $ 0.62 $ 0.62 $ 1.86 $ 1.86 Total dividends declared $ 74,195 $ 58,793 $ 210,369 $ 176,374 Earnings Per Share We calculate our basic and diluted earnings per share using the two-class The following table sets forth the calculation of basic and diluted net income per share of class A common stock based on the weighted-average of both restricted and unrestricted class A common stock outstanding ($ in thousands, except per share data): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Net income (1) $ 78,165 $ 57,722 $ 211,436 $ 159,741 Weighted-average shares outstanding, basic and diluted 116,203,140 95,013,087 111,251,864 95,004,188 Per share amount, basic and diluted $ 0.67 $ 0.61 $ 1.90 $ 1.68 (1) Represents net income attributable to Blackstone Mortgage Trust, Inc. Other Balance Sheet Items Accumulated Other Comprehensive Loss As of September 30, 2018, total accumulated other comprehensive loss was $32.8 million, primarily representing (i) $87.1 million of cumulative unrealized currency translation adjustments on assets and liabilities denominated in foreign currencies and (ii) an offsetting $54.3 million of net realized and unrealized gains related to changes in the fair value of derivative instruments. As of December 31, 2017, total accumulated other comprehensive loss was $29.7 million, primarily representing (i) $60.3 million of cumulative unrealized currency translation adjustments on assets and liabilities denominated in foreign currencies and (ii) an offsetting $30.6 million of net realized and unrealized gains related to changes in the fair value of derivative instruments. Non-Controlling The non-controlling non-controlling non-controlling non-controlling

Other Expenses

Other Expenses	9 Months Ended
	Sep. 30, 2018
Other Income and Expenses [Abstract]
Other Expenses	11. OTHER EXPENSES Our other expenses consist of the management and incentive fees we pay to our Manager and our general and administrative expenses. Management and Incentive Fees Pursuant to a management agreement between our Manager and us, or our Management Agreement, our Manager earns a base management fee in an amount equal to 1.50% per annum multiplied by our outstanding equity balance, as defined in the Management Agreement. In addition, our Manager is entitled to an incentive fee in an amount equal to the product of (i) 20% and (ii) the excess of (a) our Core Earnings (as defined in our Management Agreement) for the previous 12-month non-cash During the three and nine months ended September 30, 2018, we incurred $12.1 million and $34.2 million, respectively, of management fees payable to our Manager, compared to $9.5 million and $28.6 million during the same periods in 2017. In addition, during the three and nine months ended September 30, 2018, we incurred $6.3 million and $22.0 million, respectively, of incentive fees payable to our Manager, compared to $3.7 million and $11.9 million during the same periods in 2017. As of September 30, 2018 and December 31, 2017 we had accrued management and incentive fees payable to our Manager of $18.4 million and $14.3 million, respectively. General and Administrative Expenses General and administrative expenses consisted of the following ($ in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Professional services (1) $ 1,022 $ 933 $ 3,383 $ 2,811 Operating and other costs (1) 687 489 2,026 1,424 Subtotal 1,709 1,422 5,409 4,235 Non-cash Restricted class A common stock earned 6,609 5,819 20,113 17,496 Director stock-based compensation 125 125 375 313 Subtotal 6,734 5,944 20,488 17,809 Total BXMT expenses 8,443 7,366 25,897 22,044 Other expenses — 53 — 175 Total general and administrative expenses $ 8,443 $ 7,419 $ 25,897 $ 22,219 (1) During the three and nine months ended September 30, 2018, we recognized an aggregate $77,000 and $302,000, respectively, of expenses related to our Multifamily Joint Venture. During both the three and nine months ended September 30, 2017, we recognized an aggregate $112,000 of expenses related to our Multifamily venture.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	12. INCOME TAXES We elected to be taxed as a REIT, effective January 1, 2003, under the Internal Revenue Code for U.S. federal income tax purposes. We generally must distribute annually at least 90% of our net taxable income, subject to certain adjustments and excluding any net capital gain, in order for U.S. federal income tax not to apply to our earnings that we distribute. To the extent that we satisfy this distribution requirement, but distribute less than 100% of our net taxable income, we will be subject to U.S. federal income tax on our undistributed taxable income. In addition, we will be subject to a 4% nondeductible excise tax if the actual amount that we pay out to our stockholders in a calendar year is less than a minimum amount specified under U.S. federal tax laws. Our qualification as a REIT also depends on our ability to meet various other requirements imposed by the Internal Revenue Code, which relate to organizational structure, diversity of stock ownership, and certain restrictions with regard to the nature of our assets and the sources of our income. Even if we qualify as a REIT, we may be subject to certain U.S. federal income and excise taxes and state and local taxes on our income and assets. If we fail to maintain our qualification as a REIT for any taxable year, we may be subject to material penalties as well as federal, state, and local income tax on our taxable income at regular corporate rates and we would not be able to qualify as a REIT for the subsequent four full taxable years. As of September 30, 2018 and December 31, 2017, we were in compliance with all REIT requirements. Securitization transactions could result in the creation of taxable mortgage pools for federal income tax purposes. As a REIT, so long as we own 100% of the equity interests in a taxable mortgage pool, we generally would not be adversely affected by the characterization of the securitization as a taxable mortgage pool. Certain categories of stockholders, however, such as foreign stockholders eligible for treaty or other benefits, stockholders with net operating losses, and certain tax-exempt During the three and nine months ended September 30, 2018, we recorded a current income tax provision of $48,000 and $272,000, respectively, primarily related to activities of our taxable REIT subsidiaries and various state and local taxes. During the three and nine months ended September 30, 2017, we recorded a current income tax provision of $83,000 and $265,000, respectively. We did not have any deferred tax assets or liabilities as of September 30, 2018 or December 31, 2017. Effective January 1, 2018, under legislation from the Tax Cuts and Jobs Act of 2017, the maximum U.S. federal corporate income tax rate was reduced from 35% to 21%. Accordingly, to the extent that the activities of our taxable REIT subsidiaries generate taxable income in future periods, they may be subject to lower U.S. federal income tax rates. We have net operating losses, or NOLs, generated by our predecessor business that may be carried forward and utilized in current or future periods. As a result of our issuance of 25,875,000 shares of class A common stock in May 2013, the availability of our NOLs is generally limited to $2.0 million per annum by change of control provisions promulgated by the Internal Revenue Service with respect to the ownership of Blackstone Mortgage Trust. As of December 31, 2017, we had estimated NOLs of $159.0 million that will expire in 2029, unless they are utilized by us prior to expiration. As of September 30, 2018, tax years 2015 through 2017 remain subject to examination by taxing authorities.

Stock-Based Incentive Plans

Stock-Based Incentive Plans	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Incentive Plans	13. STOCK-BASED INCENTIVE PLANS We are externally managed by our Manager and do not currently have any employees. However, as of September 30, 2018, our Manager, certain individuals employed by an affiliate of our Manager, and certain members of our board of directors were compensated, in part, through the issuance of stock-based instruments. We had stock-based incentive awards outstanding or available to be awarded under nine benefit plans as of September 30, 2018: (i) our amended and restated 1997 non-employee Our Expired Plans have expired and no new awards may be issued under them. Under our Current Plans, a maximum of 5,000,000 shares of our class A common stock may be issued to our Manager, our directors and officers, and certain employees of affiliates of our Manager. As of September 30, 2018, we have not granted any shares under the Current Plans. The following table details the movement in our outstanding shares of restricted class A common stock and the weighted-average grant date fair value per share: Restricted Class A Weighted-Average Balance as of December 31, 2017 1,484,175 $ 30.61 Granted 318,741 31.83 Vested (404,241 ) 28.89 Forfeited (17,820 ) 30.44 Balance as of September 30, 2018 1,380,855 $ 31.40 These shares generally vest in installments over a three-year period, pursuant to the terms of the respective award agreements and the terms of the Current Plans. The 1,380,855 shares of restricted class A common stock outstanding as of September 30, 2018 will vest as follows: 448,474 shares will vest in 2018; 616,168 shares will vest in 2019; and 316,213 shares will vest in 2020. As of September 30, 2018, total unrecognized compensation cost relating to nonvested share-based compensation arrangements was $33.9 million based on the closing price of our class A common stock of $31.43 on June 29, 2018, the last trading day prior to our adoption of ASU 2018-07. 2018-07 2018-07.

Fair Values

Fair Values	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Values	14. FAIR VALUES Assets and Liabilities Measured at Fair Value The following table summarizes our assets and liabilities measured at fair value on a recurring basis ($ in thousands): September 30, 2018 December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Derivatives $ — $ 2,719 $ — $ 2,719 $ — $ 1,214 $ — $ 1,214 Liabilities Derivatives $ — $ 3,676 $ — $ 3,676 $ — $ 4,911 $ — $ 4,911 Refer to Note 2 for further discussion regarding fair value measurement. Fair Value of Financial Instruments As discussed in Note 2, GAAP requires disclosure of fair value information about financial instruments, whether or not recognized in the statement of financial position, for which it is practicable to estimate that value. The following table details the book value, face amount, and fair value of the financial instruments described in Note 2 ($ in thousands): September 30, 2018 December 31, 2017 Book Face Fair Book Face Fair Value Amount Value Value Amount Value Financial assets Cash and cash equivalents $ 86,987 $ 86,987 $ 86,987 $ 69,654 $ 69,654 $ 69,654 Restricted cash — — — 32,864 32,864 32,864 Loans receivable, net 12,176,516 12,260,103 12,261,013 10,056,732 10,108,226 10,112,331 Debt securities held-to-maturity (1) 96,050 99,000 97,607 — — — Financial liabilities Secured debt agreements, net 6,841,759 6,862,256 6,862,256 5,273,855 5,290,536 5,290,536 Loan participations sold, net 81,044 81,170 81,170 80,415 80,706 80,706 Securitized debt obligations, net 1,284,362 1,292,120 1,297,032 1,282,412 1,292,120 1,292,589 Convertible notes, net 780,951 794,828 832,407 563,911 575,000 610,201 (1) Included in other assets on our consolidated balance sheets. Estimates of fair value for cash and cash equivalents, restricted cash, and convertible notes are measured using observable, quoted market prices, or Level 1 inputs. Estimates of fair value for debt securities held-to-maturity

Variable Interest Entities

Variable Interest Entities	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	15. VARIABLE INTEREST ENTITIES Consolidated Variable Interest Entities We have financed a portion of our loans through the CLO and the 2017 Single Asset Securitization, both of which are VIEs. We are the primary beneficiary and consolidate the CLO and the 2017 Single Asset Securitization on our balance sheet as we (i) control the relevant interests of the CLO and the 2017 Single Asset Securitization that give us power to direct the activities that most significantly affect the CLO and the 2017 Single Asset Securitization, and (ii) have the right to receive benefits and obligation to absorb losses of the CLO and the 2017 Single Asset Securitization through the subordinate interests we own. The following table details the assets and liabilities of our consolidated CLO and 2017 Single Asset Securitization VIEs ($ in thousands): September 30, 2018 Assets: Loans receivable, net $ 1,500,000 $ 1,500,000 Other assets 4,899 2,407 Total assets $ 1,504,899 $ 1,502,407 Liabilities: Securitized debt obligations, net $ 1,284,362 $ 1,282,412 Other liabilities 1,869 1,379 Total liabilities $ 1,286,231 $ 1,283,791 Assets held by these VIEs are restricted and can be used only to settle obligations of the VIEs, including the subordinate interests owned by us. The liabilities of these VIEs are non-recourse Non-Consolidated In the third quarter of 2018, we contributed a $517.5 million loan to the $1.0 billion 2018 Single Asset Securitization, which is a VIE, and invested in the related $99.0 million subordinate risk retention position. We are not the primary beneficiary of the VIE because we do not have the power to direct the activities that most significantly affect the VIE’s economic performance and, therefore, do not consolidate the 2018 Single Asset Securitization on our balance sheet. We have classified the subordinate risk retention position as a held-to-maturity We are not obligated to provide, have not provided, and do not intend to provide financial support to these consolidated and non-consolidated

Transactions with Related Parti

Transactions with Related Parties	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Transactions with Related Parties	16. TRANSACTIONS WITH RELATED PARTIES We are managed by our Manager pursuant to the Management Agreement, the current term of which expires on December 19, 2018, and will be automatically renewed for a one-year As of September 30, 2018 and December 31, 2017, our consolidated balance sheet included $18.4 million and $14.3 million of accrued management and incentive fees payable to our Manager, respectively. During the three and nine months ended September 30, 2018, we paid management and incentive fees of $22.4 million and $52.2 million, respectively, to our Manager, compared to $14.4 million and $40.1 million during the same periods of 2017. In addition, during the three and nine months ended September 30, 2018, we reimbursed our Manager for expenses incurred on our behalf of $167,000 and $572,000, respectively, compared to $59,000 and $325,000 during the same periods of 2017. As of September 30, 2018, our Manager held 675,333 shares of unvested restricted class A common stock, which had an aggregate grant date fair value of $21.2 million, and vest in installments over three years from the date of issuance. During the three and nine months ended September 30, 2018, we recorded non-cash An affiliate of our Manager is the special servicer of the CLO. This affiliate did not earn any special servicing fees related to the CLO during the nine months ended September 30, 2018 or 2017. In March of 2018, we originated €1.0 billion of a total €7.3 billion senior term facility, or the Senior Term Facility, for the acquisition of a portfolio of Spanish real estate assets and a Spanish real estate management and loan servicing company by a joint venture between Banco Santander S.A. and certain Blackstone-advised investment vehicles. These investment vehicles own 51% of the joint venture, and we will forgo all non-economic rights In the first quarter of 2018, we originated a $330.0 million senior loan, the proceeds of which were used by the borrower to repay an existing loan owned by a Blackstone-advised investment vehicle. In the second quarter of 2018, we acquired from an unaffiliated third-party a 50% interest in a $1.0 billion senior loan to a borrower that is partially owned by a Blackstone-advised investment vehicle. In the third quarter of 2018, we contributed this loan to the 2018 Single Asset Securitization and invested in the related subordinate risk retention position. We will forgo all non-economic During the nine months ended September 30, 2018 and 2017, we originated three loans and five loans, respectively, whereby each respective borrower engaged an affiliate of our Manager to act as title insurance agent in connection with each transaction. We did not incur any expenses or receive any revenues as a result of these transactions. During the three and nine months ended September 30, 2018, we incurred $90,000 and $384,000, respectively, of expenses for various administrative, compliance, and capital market data services to third-party service providers that are affiliates of our Manager, compared to $87,000 and $254,000 during the same periods of 2017. In July 2018, in a fully subscribed offering totaling $1.0 billion, certain Blackstone-advised investment vehicles purchased, in the aggregate, $116.1 million of securitized debt obligations issued by the 2018 Single Asset Securitization. In June 2017, in a fully subscribed offering totaling $474.6 million, certain Blackstone-advised investment vehicles purchased, in the aggregate, $72.9 million of securitized debt obligations issued by the 2017 Single Asset Securitization. These investments by the Blackstone-advised investment vehicles represented minority participations in any individual tranche and were purchased by the Blackstone-advised investment vehicles from third-party investment banks on market terms negotiated by the majority third-party investors.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	17. COMMITMENTS AND CONTINGENCIES Unfunded Commitments Under Loans Receivable As of September 30, 2018, we had unfunded commitments of $3.0 billion related to 80 loans receivable, which amounts will generally be funded to finance our borrowers’ construction or development of real estate-related assets, capital improvements of existing assets, or lease-related expenditures. These commitments will generally be funded over the term of each loan, subject in certain cases to an expiration date. Principal Debt Repayments Our contractual principal debt repayments as of September 30, 2018 were as follows ($ in thousands): Payment Timing Total Less Than 1 Year 1 to 3 Years 3 to 5 Years More Than 5 Years Principal repayments under secured debt agreements (1) $ 6,862,256 $ 273,254 $ 2,393,008 $ 4,112,794 $ 83,200 Principal repayments of convertible notes (2) 794,828 172,328 — 622,500 — Total (3) $ 7,657,084 $ 445,582 $ 2,393,008 $ 4,735,294 $ 83,200 (1) The allocation of repayments under our secured debt agreements is based on the earlier of (i) the maturity date of each facility, or (ii) the maximum maturity date of the collateral loans, assuming all extension options are exercised by the borrower. (2) Reflects the outstanding principal balance of convertible notes, excluding any potential conversion premium. Refer to Note 8 for further details on our convertible notes. (3) As of September 30, 2018, the total does not include $81.2 million of loan participations sold, $466.7 million of non-consolidated Litigation From time to time, we may be involved in various claims and legal actions arising in the ordinary course of business. As of September 30, 2018, we were not involved in any material legal proceedings. Board of Directors’ Compensation As of September 30, 2018, of the eight members of our board of directors, our five independent directors are entitled to annual compensation of $175,000 each, $75,000 of which will be paid in the form of cash and $100,000 in the form of deferred stock units. The other three board members, including our chairman and our chief executive officer, serve as directors with no compensation. In addition, (i) the chair of our audit committee receives additional annual cash compensation of $20,000, (ii) the other members of our audit committee receive additional annual cash compensation of $10,000, and (iii) the chairs of each of our compensation and corporate governance committees receive additional annual cash compensation of $10,000.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include, on a consolidated basis, our accounts, the accounts of our wholly-owned subsidiaries, majority-owned subsidiaries, and variable interest entities, or VIEs, of which we are the primary beneficiary. All intercompany balances and transactions have been eliminated in consolidation.
Principles of Consolidation	Principles of Consolidation We consolidate all entities that we control through either majority ownership or voting rights. In addition, we consolidate all VIEs of which we are considered the primary beneficiary. VIEs are defined as entities in which equity investors (i) do not have the characteristics of a controlling financial interest and/or (ii) do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties. The entity that consolidates a VIE is known as its primary beneficiary and is generally the entity with (i) the power to direct the activities that most significantly affect the VIE’s economic performance and (ii) the right to receive benefits from the VIE or the obligation to absorb losses of the VIE that could be significant to the VIE. In the third quarter of 2018, we contributed a loan to a single asset securitization vehicle, or the 2018 Single Asset Securitization, which is a VIE, and invested in the related subordinate risk retention position. We are not the primary beneficiary of the VIE because we do not have the power to direct the activities that most significantly affect the VIE’s economic performance and, therefore, do not consolidate the 2018 Single Asset Securitization on our balance sheet. We have classified the subordinate risk retention position as a held-to-maturity In April 2017, we entered into a joint venture, or our Multifamily Joint Venture, with Walker & Dunlop Inc. to originate, hold, and finance multifamily bridge loans. Pursuant to the terms of the agreements governing the joint venture, Walker & Dunlop contributed 15% of the venture’s equity capital and we contributed 85%. We consolidate the Multifamily Joint Venture as we have a controlling financial interest. The non-controlling non-controlling
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may ultimately differ from those estimates.
Revenue Recognition	Revenue Recognition Interest income from our loans receivable portfolio and debt securities is recognized over the life of each investment using the effective interest method and is recorded on the accrual basis. Recognition of fees, premiums, and discounts associated with these investments is deferred and recorded over the term of the loan or debt security as an adjustment to yield. Income accrual is generally suspended for loans at the earlier of the date at which payments become 90 days past due or when, in the opinion of our Manager, recovery of income and principal becomes doubtful. Income is then recorded on the basis of cash received until accrual is resumed when the loan becomes contractually current and performance is demonstrated to be resumed. In addition, for loans we originate, the related origination expenses are deferred and recognized as a component of interest income, however expenses related to loans we acquire are included in general and administrative expenses as incurred.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash Cash and cash equivalents represent cash held in banks and liquid investments with original maturities of three months or less. We may have bank balances in excess of federally insured amounts; however, we deposit our cash and cash equivalents with high credit-quality institutions to minimize credit risk exposure. We have not experienced, and do not expect, any losses on our cash or cash equivalents. Restricted cash represents cash held in a segregated bank account related to a letter of credit. The following table provides a reconciliation of cash, cash equivalents, and restricted cash in our consolidated balance sheets to the total amount shown in our consolidated statements of cash flows ($ in thousands): September 30, 2018 September 30, 2017 Cash and cash equivalents $ 86,987 $ 61,221 Restricted cash — 32,864 Total cash, cash equivalents, and restricted cash shown in our consolidated statements of cash flows $ 86,987 $ 94,085
Loans Receivable and Provision for Loan Losses	Loans Receivable and Provision for Loan Losses We originate and purchase commercial real estate debt and related instruments generally to be held as long-term investments at amortized cost. We are required to periodically evaluate each of these loans for possible impairment. Impairment is indicated when it is deemed probable that we will not be able to collect all amounts due to us pursuant to the contractual terms of the loan. If a loan is determined to be impaired, we write down the loan through a charge to the provision for loan losses. Impairment of these loans, which are collateral dependent, is measured by comparing the estimated fair value of the underlying collateral, less costs to sell, to the book value of the respective loan. These valuations require significant judgments, which include assumptions regarding capitalization rates, leasing, creditworthiness of major tenants, occupancy rates, availability of financing, exit plan, loan sponsorship, actions of other lenders, and other factors deemed necessary by our Manager. Actual losses, if any, could ultimately differ from these estimates. Our Manager performs a quarterly review of our portfolio of loans. In conjunction with this review, our Manager assesses the risk factors of each loan, and assigns it a risk rating based on a variety of factors, including, without limitation, loan-to-value 5-point 1 - Very Low Risk 2 - Low Risk 3 - Medium Risk 4 - High Risk/Potential for Loss: 5 - Impaired/Loss Likely: During the second quarter of 2015, we acquired a portfolio of loans from General Electric Capital Corporation and certain of its affiliates, or the GE portfolio, for a total purchase price of $4.7 billion. We allocated the aggregate purchase price between each loan based on its fair value relative to the overall portfolio, which allocation resulted in purchase discounts or premiums determined on an asset-by-asset
Debt Securities Held-to-Maturity	Debt Securities Held-to-Maturity We classify our debt securities as held-to-maturity, If, based on current information and events, there is an adverse change in cash flows expected to be collected from the cash flows previously projected for one of our debt securities, an other-than-temporary impairment is deemed to have occurred. A change in expected cash flows is considered adverse if the present value of the revised cash flows (taking into consideration both the timing and amount of cash flows expected to be collected), discounted using the debt security’s current yield, is less than the present value of the previously estimated remaining cash flows. If an other-than-temporary impairment is considered to have occurred, the debt security is written down to fair value. The total other-than-temporary impairment is bifurcated into (i) the amount related to expected credit losses, and (ii) the amount related to fair value adjustments in excess of expected credit losses. The other-than-temporary impairment related to expected credit losses is calculated by comparing the amortized cost basis of the security to the present value of cash flows expected to be collected, discounted at the security’s current yield, and is recognized in earnings in the consolidated statement of operations. The remaining other-than-temporary impairment that is not related to expected credit losses is recognized in other comprehensive income (loss). A portion of other-than-temporary impairments recognized through earnings is accreted back to the amortized cost basis of the security through interest income, while amounts recognized through other comprehensive income (loss) are amortized over the life of the security with no impact on earnings.
Derivative Financial Instruments	Derivative Financial Instruments We classify all derivative financial instruments as either other assets or other liabilities on our consolidated balance sheets at fair value. On the date we enter into a derivative contract, we designate each contract as (i) a hedge of a net investment in a foreign operation, or net investment hedge, (ii) a hedge of a forecasted transaction or of the variability of cash flows to be received or paid related to a recognized asset or liability, or cash flow hedge, (iii) a hedge of a recognized asset or liability, or fair value hedge, or (iv) a derivative instrument not to be designated as a hedging derivative, or non-designated non-designated On a quarterly basis, we also formally assess whether the derivative we designated in each hedging relationship is expected to be, and has been, highly effective in offsetting changes in the value or cash flows of the hedged items. If it is determined that a derivative is not highly effective at hedging the designated exposure, hedge accounting is discontinued and the changes in fair value of the instrument are included in net income prospectively. Changes in the fair value of our derivative instruments that qualify as hedges are reported as a component of accumulated other comprehensive income (loss) on our consolidated financial statements. Deferred gains and losses are reclassified out of accumulated other comprehensive income (loss) and into net income in the same period or periods during which the hedged transaction affects earnings, and are presented in the same line item as the earnings effect of the hedged item. For cash flow hedges, this is typically when the periodic swap settlements are made, while for net investment hedges, this occurs when the hedged item is sold or substantially liquidated. To the extent a derivative does not qualify for hedge accounting and is deemed a non-designated
Secured Debt Agreements	Secured Debt Agreements Where applicable, we record investments financed with repurchase agreements as separate assets and the related borrowings under any repurchase agreements are recorded as separate liabilities on our consolidated balance sheets. Interest income earned on the investments and interest expense incurred on the repurchase agreements are reported separately on our consolidated statements of operations.
Senior Loan Participations	Senior Loan Participations In certain instances, we finance our loans through the non-recourse non-consolidated
Convertible Notes	Convertible Notes The “Debt with Conversion and Other Options” Topic of the Financial Accounting Standards Board, or FASB, Accounting Standards Codification, or ASC, requires the liability and equity components of convertible debt instruments that may be settled in cash upon conversion, including partial cash settlement, to be separately accounted for in a manner that reflects the issuer’s nonconvertible debt borrowing rate. The initial proceeds from the sale of convertible notes are allocated between a liability component and an equity component in a manner that reflects interest expense at the rate of similar nonconvertible debt that could have been issued at such time. The equity component represents the excess initial proceeds received over the fair value of the liability component of the notes as of the date of issuance. We measured the estimated fair value of the debt component of our convertible notes as of the respective issuance dates based on our nonconvertible debt borrowing rate. The equity component of each series of our convertible notes is reflected within additional paid-in non-cash non-cash
Deferred Financing Costs	Deferred Financing Costs The deferred financing costs that are included as a reduction in the net book value of the related liability on our consolidated balance sheets include issuance and other costs related to our debt obligations. These costs are amortized as interest expense using the effective interest method over the life of the related obligations.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The “Fair Value Measurements and Disclosures” Topic of the FASB, or ASC 820, defines fair value, establishes a framework for measuring fair value, and requires certain disclosures about fair value measurements under GAAP. Specifically, this guidance defines fair value based on exit price, or the price that would be received upon the sale of an asset or the transfer of a liability in an orderly transaction between market participants at the measurement date. ASC 820 also establishes a fair value hierarchy that prioritizes and ranks the level of market price observability used in measuring financial instruments. Market price observability is affected by a number of factors, including the type of financial instrument, the characteristics specific to the financial instrument, and the state of the marketplace, including the existence and transparency of transactions between market participants. Financial instruments with readily available quoted prices in active markets generally will have a higher degree of market price observability and a lesser degree of judgment used in measuring fair value. Financial instruments measured and reported at fair value are classified and disclosed based on the observability of inputs used in the determination, as follows: • Level 1: Generally includes only unadjusted quoted prices that are available in active markets for identical financial instruments as of the reporting date. • Level 2: Pricing inputs include quoted prices in active markets for similar instruments, quoted prices in less active or inactive markets for identical or similar instruments where multiple price quotes can be obtained, and other observable inputs, such as interest rates, yield curves, credit risks, and default rates. • Level 3: Pricing inputs are unobservable for the financial instruments and include situations where there is little, if any, market activity for the financial instrument. These inputs require significant judgment or estimation by management of third-parties when determining fair value and generally represent anything that does not meet the criteria of Levels 1 and 2. The estimated value of each asset reported at fair value using Level 3 inputs is determined by an internal committee composed of members of senior management of our Manager, including our Chief Executive Officer, Chief Financial Officer, and other senior officers. Certain of our other assets are reported at fair value either (i) on a recurring basis, as of each quarter-end, We are also required by GAAP to disclose fair value information about financial instruments, which are not otherwise reported at fair value in our consolidated balance sheet, to the extent it is practicable to estimate a fair value for those instruments. These disclosure requirements exclude certain financial instruments and all non-financial The following methods and assumptions are used to estimate the fair value of each class of financial instruments, for which it is practicable to estimate that value: • Cash and cash equivalents: The carrying amount of cash and cash equivalents approximates fair value. • Restricted cash: The carrying amount of restricted cash approximates fair value. • Loans receivable, net: The fair values of these loans were estimated by our Manager based on a discounted cash flow methodology, taking into consideration various factors including capitalization rates, discount rates, leasing, occupancy rates, availability and cost of financing, exit plan, sponsorship, actions of other lenders, and indications of market value from other market participants. • Debt securities held-to-maturity: • Derivative financial instruments: The fair value of our foreign currency and interest rate contracts was estimated using advice from a third-party derivative specialist, based on contractual cash flows and observable inputs comprising foreign currency rates and credit spreads. • Secured debt agreements, net: The fair value of these instruments was estimated based on the rate at which a similar credit facility would currently be priced. • Loan participations sold, net: The fair value of these instruments was estimated based on the value of the related loan receivable asset. • Securitized debt obligations, net: The fair value of these instruments was estimated by utilizing third-party pricing service providers. In determining the 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. • Convertible notes, net: Each series of the convertible notes is actively traded and their fair values were obtained using quoted market prices.
Income Taxes	Income Taxes Our financial results generally do not reflect provisions for current or deferred income taxes on our REIT taxable income. We believe that we operate in a manner that will continue to allow us to be taxed as a REIT and, as a result, we generally do not expect to pay substantial corporate level taxes other than those payable by our taxable REIT subsidiaries. If we were to fail to meet these requirements, we may be subject to federal, state, and local income tax on current and past income, and penalties. Refer to Note 12 for additional information.
Stock-Based Compensation	Stock-Based Compensation Our stock-based compensation consists of awards issued to our Manager and certain individuals employed by an affiliate of our Manager that vest over the life of the awards, as well as deferred stock units issued to certain members of our board of directors. Stock-based compensation expense is recognized for these awards in net income on a variable basis over the applicable vesting period of the awards, based on the value of our class A common stock. Refer to Note 13 for additional information.
Earnings per Share	Earnings per Share Basic earnings per share, or Basic EPS, is computed in accordance with the two-class two-class Diluted earnings per share, or Diluted EPS, is determined using the treasury stock method, and is based on the net earnings allocable to our class A common stock, including restricted class A common stock and deferred stock units, divided by the weighted-average number of shares of our class A common stock, including restricted class A common stock and deferred stock units. Refer to Note 10 for additional discussion of earnings per share.
Foreign Currency	Foreign Currency In the normal course of business, we enter into transactions not denominated in United States, or U.S., dollars. Foreign exchange gains and losses arising on such transactions are recorded as a gain or loss in our consolidated statements of operations. In addition, we consolidate entities that have a non-U.S. Non-U.S. non-U.S.
Underwriting Commissions and Offering Costs	Underwriting Commissions and Offering Costs Underwriting commissions and offering costs incurred in connection with common stock offerings are reflected as a reduction of additional paid-in
Recent Accounting Pronouncements	Recent Accounting Pronouncements In June 2018, the FASB issued ASU 2018-07 2018-07. 2018-07 2018-07, 2018-07 2018-07 In June 2016, the FASB issued ASU 2016-13 “Financial ASU 2016-13. ASU 2016-13 significantly ASU 2016-13 will for available-for-sale debt ASU 2016-13 is ASU 2016-13 will In May 2014, the FASB issued ASU 2014-09, “Revenue , or ASU 2014-09. ASU 2014-09 broadly recognition. ASU 2014-09 is ASU 2014-09 in

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash in our consolidated balance sheets to the total amount shown in our consolidated statements of cash flows ($ in thousands): September 30, 2018 September 30, 2017 Cash and cash equivalents $ 86,987 $ 61,221 Restricted cash — 32,864 Total cash, cash equivalents, and restricted cash shown in our consolidated statements of cash flows $ 86,987 $ 94,085

Loans Receivable, Net (Tables)

Loans Receivable, Net (Tables)	9 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Overall Statistics for Loans Receivable Portfolio	The following table details overall statistics for our loans receivable portfolio ($ in thousands): September 30, 2018 December 31, 2017 Number of loans 112 110 Principal balance $ 12,260,103 $ 10,108,226 Net book value $ 12,176,516 $ 10,056,732 Unfunded loan commitments (1) $ 3,046,350 $ 1,573,107 Weighted-average cash coupon (2) 5.61 % 5.55 % Weighted-average all-in (2) 5.94 % 5.95 % Weighted-average maximum maturity (years) (3) 3.8 3.5 (1) Unfunded commitments will primarily be funded to finance our borrowers’ construction or development of real estate-related assets, capital improvements of existing assets, or lease-related expenditures. These commitments will generally be funded over the term of each loan, subject in certain cases to an expiration date. (2) Our floating rate loans are indexed to various benchmark rates, with 83% and 92% of our floating rate loans by principal balance indexed to USD LIBOR as of September 30, 2018 and December 31, 2017, respectively. In addition to cash coupon, all-in all-in (3) Maximum maturity assumes all extension options are exercised by the borrower, however our loans may be repaid prior to such date. As of September 30, 2018, 86% of our loans by principal balance were subject to yield maintenance or other prepayment restrictions and 14% were open to repayment by the borrower without penalty. As of December 31, 2017, 75% of our loans were subject to yield maintenance or other prepayment restrictions and 25% were open to repayment by the borrower without penalty.
Activity Relating to Loans Receivable Portfolio	Activity relating to our loans receivable portfolio was as follows ($ in thousands): Principal Balance Deferred Fees / Other Items (1) Net Book Value December 31, 2017 $ 10,108,226 $ (51,494 ) $ 10,056,732 Loan fundings 5,222,803 — 5,222,803 Loan repayments (2,452,811 ) — (2,452,811 ) Loan contributed to securitization (517,500 ) 5,498 (512,002 ) Unrealized (loss) gain on foreign currency translation (100,615 ) 678 (99,937 ) Deferred fees and other items — (74,111 ) (74,111 ) Amortization of fees and other items — 35,842 35,842 September 30, 2018 $ 12,260,103 $ (83,587 ) $ 12,176,516 (1) Other items primarily consist of purchase discounts or premiums, exit fees, and deferred origination expenses.
Property Type and Geographic Distribution of Properties Securing Loans in Portfolio	The tables below detail the property type and geographic distribution of the properties securing the loans in our portfolio ($ in thousands): September 30, 2018 Property Type Number of Net Book Value Total Loan Exposure (1)(2) Percentage of Portfolio Office 49 $ 5,956,675 $ 6,006,534 47% Hotel 15 1,992,889 2,069,818 16 Multifamily 32 1,894,001 1,903,572 15 Spanish Assets 1 1,152,487 1,160,400 9 Retail 4 336,787 337,334 3 Condominium 2 84,429 158,462 1 Other 9 759,248 1,090,711 9 112 $ 12,176,516 $ 12,726,831 100% Geographic Location Number of Net Book Value Total Loan (1)(2) Percentage of United States Northeast 30 $ 3,796,633 $ 3,830,021 29% West 25 2,543,743 2,637,582 21 Southeast 18 2,025,381 2,034,852 16 Midwest 8 901,310 906,102 7 Southwest 13 477,809 480,792 4 Northwest 2 141,199 141,630 1 Subtotal 9,886,075 10,030,979 78 International Spain 1 1,152,487 1,160,400 9 United Kingdom 5 492,790 837,688 7 Canada 5 335,957 332,841 3 Australia 2 218,286 220,335 2 Belgium 1 71,494 71,945 1 Germany 1 11,814 65,000 — Netherlands 1 7,613 7,643 — Subtotal 16 2,290,441 2,695,852 22 Total 112 $ 12,176,516 $ 12,726,831 100% (1) In certain instances, we finance our loans through the non-recourse non-consolidated (2) Excludes investment exposure to the $1.0 billion 2018 Single Asset Securitization. See Note 4 for details of the subordinated risk retention interest we own in the 2018 Single Asset Securitization. December 31, 2017 Property Type Number of Net Book Value Total Loan (1) Percentage of Office 53 $ 5,773,972 $ 5,807,170 53% Hotel 15 1,830,568 1,905,497 17 Multifamily 25 1,220,423 1,228,959 11 Retail 6 487,473 940,980 8 Condominium 2 142,342 268,751 2 Other 9 601,954 942,251 9 110 $ 10,056,732 $ 11,093,608 100% Geographic Location Number of Net Book Value Total Loan (1) Percentage of United States Northeast 26 $ 2,857,948 $ 2,871,219 26% West 29 2,672,069 2,816,276 24 Southeast 17 2,007,202 2,470,992 22 Midwest 9 856,559 862,578 8 Southwest 10 380,204 380,120 3 Northwest 2 283,381 286,221 3 Subtotal 93 9,057,363 9,687,406 86 International United Kingdom 6 440,317 794,789 7 Canada 7 415,893 412,343 4 Belgium 1 73,779 74,431 1 Germany 1 12,237 67,399 1 Netherlands 2 57,143 57,240 1 Subtotal 17 999,369 1,406,202 14 Total 110 $ 10,056,732 $ 11,093,608 100% (1) In certain instances, we finance our loans through the non-recourse non-consolidated
Principal Balance and Net Book Value of Loans Receivable Based on Internal Risk Ratings	The following table allocates the principal balance and net book value of our loans receivable based on our internal risk ratings ($ in thousands): September 30, 2018 December 31, 2017 Risk Rating Number of Loans Net Book Value Total Loan Exposure (1)(2) Risk Rating Number of Loans Net Book Value Total Loan Exposure (1) 1 1 $ 53,849 $ 53,873 1 1 $ 31,842 $ 31,890 2 43 4,167,871 4,272,068 2 41 3,512,709 3,521,701 3 68 7,954,796 8,400,890 3 67 6,491,617 7,519,465 4 — — — 4 1 20,564 20,552 5 — — — 5 — — — 112 $ 12,176,516 $ 12,726,831 110 $ 10,056,732 $ 11,093,608 (1) In certain instances, we finance our loans through the non-recourse non-consolidated (2) Excludes investment exposure to the $1.0 billion 2018 Single Asset Securitization. See Note 4 for details of the subordinated risk retention interest we own in the 2018 Single Asset Securitization.

Other Assets and Liabilities (T

Other Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Summary of Components of Other Assets	The following table details the components of our other assets ($ in thousands): September 30, 2018 December 31, 2017 Debt securities held-to-maturity (1) $ 96,050 $ — Accrued interest receivable 45,762 38,573 Collateral deposited under derivative agreements 7,360 4,120 Loan portfolio payments held by servicer (2) 3,902 54,759 Derivative assets 2,719 1,214 Prepaid expenses 151 798 Prepaid taxes 28 31 Other — 80 Total $ 155,972 $ 99,575 (1) Represents a $99.0 million subordinate risk retention interest in the $1.0 billion 2018 Single Asset Securitization, with a yield to full maturity of L+10.0% and a maximum maturity date of June 9, 2025, assuming all extension options are exercised by the borrower. Refer to Note 15 for additional discussion. (2) Represents loan principal and interest payments held by our third-party loan servicer as of the balance sheet date which were remitted to us during the subsequent remittance cycle.
Summary of Components of Other Liabilities	The following table details the components of our other liabilities ($ in thousands): September 30, 2018 December 31, 2017 Accrued dividends payable $ 74,195 $ 66,888 Accrued interest payable 23,701 14,162 Accrued management and incentive fees payable 18,368 14,284 Derivative liabilities 3,676 4,911 Accounts payable and other liabilities 3,426 2,125 Secured debt repayments pending servicer remittance (1) — 38,456 Total $ 123,366 $ 140,826 (1) Represents pending transfers from our third-party loan servicer that were remitted to our banking counterparties during the subsequent remittance cycle.

Secured Debt Agreements, Net (T

Secured Debt Agreements, Net (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of Secured Debt Agreements	The following table details our secured debt agreements ($ in thousands): Secured Debt Agreements Borrowings Outstanding September 30, 2018 December 31, 2017 Credit facilities $ 4,850,911 $ 4,068,249 Asset-specific financings 1,499,286 518,864 GE portfolio acquisition facility 512,059 703,423 Revolving credit agreement — — Total secured debt agreements $ 6,862,256 $ 5,290,536 Deferred financing costs (1) (20,497 ) (16,681 ) Net book value of secured debt $ 6,841,759 $ 5,273,855 (1) Costs incurred in connection with our secured debt agreements are recorded on our consolidated balance sheet when incurred and recognized as a component of interest expense over the life of each related agreement.
Credit Facilities	The following tables detail our credit facilities ($ in thousands): September 30, 2018 Maximum Credit Borrowings Collateral Lender Facility Size (1) Potential (2) Outstanding Available (2) Assets (3) Bank of America $ 1,000,000 $ 863,592 $ 863,592 $ — $ 1,091,860 Wells Fargo 2,000,000 1,160,678 850,687 309,991 1,577,251 MetLife 1,000,000 737,770 737,770 — 946,933 Barclays 1,000,000 617,360 617,360 — 771,700 Citibank (4) 750,000 576,369 480,129 96,240 730,723 JP Morgan 500,000 435,095 332,909 102,186 564,070 Morgan Stanley (5) 651,550 329,256 278,770 50,486 461,760 Deutsche Bank 500,000 277,247 277,247 — 380,986 Société Générale (6) 464,160 235,229 235,229 — 298,951 Goldman Sachs - Multi. JV (7) 250,000 117,498 117,498 — 148,099 Bank of America - Multi. JV (7) 200,000 59,720 59,720 — 74,650 $ 8,315,710 $ 5,409,814 $ 4,850,911 $ 558,903 $ 7,046,983 December 31, 2017 Maximum Credit Borrowings Collateral Lender Facility Size (1) Potential (2) Outstanding Available (2) Assets (3) Wells Fargo $ 2,000,000 $ 1,289,135 $ 1,170,801 $ 118,334 $ 1,680,325 MetLife 1,000,000 807,164 807,164 — 1,039,231 Bank of America 750,000 573,542 573,542 — 765,049 JP Morgan 500,000 443,496 319,755 123,741 579,218 Société Générale (6) 480,200 300,871 300,871 — 373,181 Deutsche Bank 500,000 295,743 295,743 — 399,203 Citibank (4) 800,125 354,354 240,881 113,473 455,433 Morgan Stanley (5) 675,650 456,344 216,044 240,300 591,168 Bank of America - Multi. JV (7) 200,000 85,560 85,560 — 106,950 Goldman Sachs - Multi. JV (7) 250,000 57,888 57,888 — 75,225 $ 7,155,975 $ 4,664,097 $ 4,068,249 $ 595,848 $ 6,064,983 (1) Maximum facility size represents the largest amount of borrowings available under a given facility once sufficient collateral assets have been approved by the lender and pledged by us. (2) Potential borrowings represents the total amount we could draw under each facility based on collateral already approved and pledged. When undrawn, these amounts are immediately available to us at our sole discretion under the terms of each credit facility. (3) Represents the principal balance of the collateral assets. (4) As of September 30, 2018, the Citibank facility was denominated in U.S. dollars. As of December 31, 2017, the maximum facility size was composed of a $500.0 million facility denominated in U.S. dollars plus a €250.0 million facility, which translated to $300.1 million as of such date. (5) As of September 30, 2018 and December 31, 2017, the Morgan Stanley maximum facility size was £500.0 million, which translated to $651.6 million and $675.7 million, respectively. (6) As of September 30, 2018 and December 31, 2017, the Société Générale maximum facility size was €400.0 million, which translated to $464.2 million and $480.2 million, respectively. (7) These facilities finance the loan investments of our consolidated Multifamily Joint Venture. Refer to Note 2 for additional discussion of our Multifamily Joint Venture.
Summary of Key Terms of Credit Facilities	The following tables outline the key terms of our credit facilities as of September 30, 2018: Lender Currency Guarantee (1) Margin Call (2) Term/Maturity Morgan Stanley $ / £ / € 25% Collateral marks only March 3, 2020 Goldman Sachs - Multi. JV (3) $ 25% Collateral marks only July 12, 2020 (4) JP Morgan $ / £ 50% Collateral marks only January 7, 2021 Bank of America - Multi. JV (3) $ 43% Collateral marks only July 19, 2021 (5) Deutsche Bank $ 32% Collateral marks only August 9, 2021 (6) Barclays $ 25% Collateral marks only March 29, 2023 (7) MetLife $ 50% Collateral marks only April 22, 2023 (8) Bank of America $ 50% Collateral marks only May 21, 2023 (9) Citibank $ / £ / € 25% Collateral marks only Term matched (10) Société Générale $ / £ / € 25% Collateral marks only Term matched (10) Wells Fargo $ 25% Collateral marks only Term matched (10) (1) Other than amounts guaranteed based on specific collateral asset types, borrowings under our credit facilities are non-recourse (2) Margin call provisions under our credit facilities do not permit valuation adjustments based on capital markets events, and are limited to collateral-specific credit marks. (3) These facilities finance the loan investments of our consolidated Multifamily Joint Venture. Refer to Note 2 for additional discussion of our Multifamily Joint Venture. (4) Includes a one-year (5) Includes two one-year (6) Includes two one-year (7) Includes four one-year (8) Includes four one-year (9) Includes two one-year (10) These credit facilities have various availability periods during which new advances can be made and which are generally subject to each lender’s discretion. Maturity dates for advances outstanding are tied to the term of each respective collateral asset. Currency Potential Outstanding Borrowings (1) Floating Rate Index Spread (2) Advance Rate (3) $ $ 5,024,025 $ 4,551,603 1-month 1.75% 79.2% € € 54,869 € 12,100 3-month 2.28% 80.0% £ £ 247,194 £ 218,914 3-month 1.97% 79.0% $ 5,409,815 $ 4,850,911 1.77% 79.2% (1) Potential borrowings represents the total amount we could draw under each facility based on collateral already approved and pledged. When undrawn, these amounts are immediately available to us at our sole discretion under the terms of each credit facility. (2) Represents weighted-average spread over the applicable floating rate index, based on borrowings outstanding. (3) Represents weighted-average advance rate based on the approved outstanding principal balance of the collateral assets pledged.
Summary of Asset-Specific Financings	The following tables detail our asset-specific financings ($ in thousands): September 30, 2018 Asset-Specific Financings Count Principal Book Value Wtd. Avg. (1) Guarantee (2) Wtd. Avg. (3) Collateral assets 5 $ 1,905,475 $ 1,895,094 L+3.61 % n/a Sep. 2022 Financing provided (4) 5 $ 1,499,286 $ 1,492,614 L+1.77 % $ 1,178,874 Sep. 2022 December 31, 2017 Asset-Specific Financings Count Principal Book Value Wtd. Avg. (1) Guarantee (2) Wtd. Avg. (3) Collateral assets 6 $ 682,259 $ 677,296 L+4.76 % n/a Dec. 2020 Financing provided (4) 6 $ 518,864 $ 517,088 L+2.50 % $ 162,475 Dec. 2020 (1) These floating rate loans and related liabilities are indexed to the various benchmark rates relevant in each arrangement in terms of currency and payment frequency. Therefore the net exposure to each benchmark rate is in direct proportion to our net assets indexed to that rate. In addition to cash coupon, yield/cost includes the amortization of deferred origination fees / financing costs. (2) Other than amounts guaranteed on an asset-by-asset basis, borrowings under our asset-specific financings are non-recourse to us. (3) The weighted-average term is determined based on the maximum maturity of the corresponding loans, assuming all extension options are exercised by the borrower. Each of our asset-specific financings are term-matched to the corresponding collateral loans. (4) As of September 30, 2018 and December 31, 2017, borrowings of $517.8 million and $394.8 million, respectively, under these asset specific financings are cross collateralized with related credit facilities with the same lenders. The weighted-average outstanding balance of our asset-specific financings was $1.3 billion for the nine months ended September 30, 2018 and $522.5 million for the nine months ended December 31, 2017. GE Portfolio Acquisition Facility During the second quarter of 2015, concurrently with our acquisition of the GE portfolio, we entered into an agreement with Wells Fargo to provide us with secured financing for the acquired portfolio. The GE portfolio acquisition facility is non-revolving September 30, 2018 GE Portfolio Acquisition Facility Count Principal (1) Book Value Wtd. Avg. (2) Guarantee (3) Wtd. Avg. (4) Collateral assets 11 $ 662,464 $ 664,189 5.92 % n/a May 2021 Financing provided 11 $ 512,059 $ 511,346 L+1.77 % $ 250,000 May 2021 December 31, 2017 GE Portfolio Acquisition Facility Count Principal (1) Book Value Wtd. Avg. (2) Guarantee (3) Wtd. Avg. (4) Collateral assets 16 $ 906,707 $ 911,092 5.74 % n/a Jul. 2020 Financing provided 16 $ 703,423 $ 702,337 L+1.72 % $ 250,000 Jul. 2020 (1) As of September 30, 2018, this facility provided for $608.7 million of financing, of which $512.1 million was outstanding and an additional $96.6 million was available to finance future loan fundings in the GE portfolio. As of December 31, 2017, this facility provided for $816.3 million of financing, of which $703.4 million was outstanding and an additional $112.9 million was available to finance future loan fundings in the GE portfolio. (2) In addition to cash coupon, yield/cost includes the amortization of deferred origination fees / financing costs. (3) We guarantee obligations under the GE portfolio acquisition facility in an amount equal to the greater of (i) 25% of outstanding asset-specific borrowings, and (ii) $250.0 million. (4) The weighted-average term is determined based on the maximum maturity of the corresponding loans, assuming all extension options are exercised by the borrower. Each of our asset-specific financings are term-matched to the corresponding collateral loans.

Loan Participations Sold, Net (

Loan Participations Sold, Net (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Summary of Statistics for Loan Participations Sold	The following tables detail our loan participations sold ($ in thousands): September 30, 2018 Loan Participations Sold Count Principal Book Value Yield/Cost (1) Guarantee (2) Term Total loan 1 $ 106,259 $ 105,149 L+6.06 % n/a Feb. 2022 Senior participation (3)(4) 1 81,170 81,044 L+4.08 % n/a Feb. 2022 December 31, 2017 Loan Participations Sold Count Principal Book Value Yield/Cost (1) Guarantee (2) Term Total loan 1 $ 141,119 $ 138,907 L+5.94 % n/a Feb. 2022 Senior participation (3)(4) 1 80,706 80,415 L+4.14 % n/a Feb. 2022 (1) Our floating rate loans and related liabilities are indexed to the various benchmark rates relevant in each arrangement in terms of currency and payment frequency. Therefore the net exposure to each benchmark rate is in direct proportion to our net assets indexed to that rate. In addition to cash coupon, yield/cost includes the amortization of deferred fees / financing costs. (2) As of September 30, 2018 and December 31, 2017, our loan participations sold was non-recourse to us. (3) During the three and nine months ended September 30, 2018, we recorded $11.7 million and $15.2 million, respectively, of interest expense related to our loan participations sold. During the three and nine months ended September 30, 2017, we recorded $4.0 million and $9.3 million, respectively, of interest expense related to our loan participations sold. (4) The difference between principal balance and book value of loan participations sold is due to deferred financing costs of $126,000 and $291,000, as of September 30, 2018 and December 31, 2017, respectively.

Securitized Debt Obligations,_2

Securitized Debt Obligations, Net (Tables)	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Schedule of Information on Securitized Debt Obligations	The following tables detail our securitized debt obligations ($ in thousands): September 30, 2018 Securitized Debt Obligations Count Principal Book Value Wtd. Avg. Yield/Cost (1) Term (2) Collateralized Loan Obligation Collateral assets 28 $ 1,000,000 $ 1,000,000 6.09 % Feb. 2022 Financing provided 1 817,500 809,944 L+1.74 % June 2035 2017 Single Asset Securitization Collateral assets (3) 1 678,963 675,437 L+3.60 % June 2023 Financing provided 1 474,620 474,418 L+1.65 % June 2033 Total Collateral assets 29 $ 1,678,963 $ 1,675,437 6.00 % Financing provided (4) 2 $ 1,292,120 $ 1,284,362 L+1.71 % December 31, 2017 Securitized Debt Obligations Count Principal Book Value Wtd. Avg. Yield/Cost (1) Term (2) Collateralized Loan Obligation Collateral assets 31 $ 1,000,000 $ 1,000,000 5.16 % Nov. 2021 Financing provided 1 817,500 808,083 L+1.76 % June 2035 2017 Single Asset Securitization Collateral assets (3) 1 656,406 652,880 L+3.60 % June 2023 Financing provided 1 474,620 474,328 L+1.94 % June 2033 Total Collateral assets 32 $ 1,656,406 $ 1,652,880 5.17 % Financing provided (4) 2 $ 1,292,120 $ 1,282,411 L+1.83 % (1) As of September 30, 2018, 98% of our loans financed by securitized debt obligations earned a floating rate of interest. As of December 31, 2017, 98% of our loans financed by securitized debt obligations earned a floating rate of interest. In addition to cash coupon, all-in All-in (2) Loan term represents weighted-average final maturity, assuming all extension options are exercised by the borrower. Repayments of securitized debt obligations are tied to timing of the related collateral loan asset repayments. The term of these obligations represents the rated final distribution date of the securitizations. (3) The collateral assets for the 2017 Single Asset Securitization include the total loan amount, of which we securitized $500.0 million. (4) During the three and nine months ended September 30, 2018, we recorded $12.5 million and $35.6 million of interest expense, respectively, related to our securitized debt obligations. During both the three and nine months ended September 30, 2017, we recorded $3.8 million of interest expense related to our securitized debt obligations.

Convertible Notes, Net (Tables)

Convertible Notes, Net (Tables)	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Summary of Outstanding Convertible Senior Note	As of September 30, 2018, the following convertible senior notes, or Convertible Notes, were outstanding ($ in thousands): Convertible Notes Issuance Face Value Coupon Rate All-in Cost (1) Conversion Rate (2) Maturity November 2013 $ 172,328 5.25 % 5.87 % 36.5472 December 1, 2018 May 2017 402,500 4.38 % 4.85 % 28.0324 May 5, 2022 March 2018 220,000 4.75 % 5.33 % 27.6052 March 15, 2023 (1) Includes issuance costs that are amortized through interest expense over the life of the Convertible Notes using the effective interest method. (2) Represents the shares of class A common stock per $1,000 principal amount of Convertible Notes, which is equivalent to a conversion price of $27.36, $35.67, and $36.23 per share of class A common stock, respectively, for the November 2013, May 2017, and March 2018 convertible notes. As a result of exceeding the cumulative dividend threshold, as defined in the November 2013 convertible notes supplemental indenture, the conversion rate on the November 2013 convertible notes was most recently adjusted on March 28, 2018 from the prior conversion rate of 36.1380 shares of class A common stock per $1,000 principal amount of convertible notes, which was equivalent to a conversion price of $27.67 per share of class A common stock. Pursuant to the terms of the November 2013 supplemental indenture, the conversion rate will be adjusted to 36.8161 on the first day of any future observation period related to a conversion of the November 2013 convertible notes to account for the dividends paid on our class A common stock on July 16, 2018 and October 15, 2018. The cumulative dividend threshold as defined in the respective May 2017 and March 2018 convertible notes supplemental indentures have not been exceeded as of September 30, 2018.
Summary of Details of Net Book Value of Convertible Note	The following table details the net book value of our Convertible Notes on our consolidated balance sheets ($ in thousands): September 30, 2018 Face value $ 794,828 $ 575,000 Unamortized discount (12,956 ) (10,279 ) Deferred financing costs (921 ) (810 ) Net book value $ 780,951 $ 563,911
Summary of Details about Interest Expense	The following table details our interest expense related to the Convertible Notes ($ in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Cash coupon $ 9,277 $ 6,247 $ 25,333 $ 12,732 Discount and issuance cost amortization 1,535 1,202 4,242 2,869 Total interest expense $ 10,812 $ 7,449 $ 29,575 $ 15,601

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of Outstanding Foreign Exchange Derivatives Designated as Net Investment Hedges of Foreign Currency Risk	The following table details our outstanding foreign exchange derivatives that were designated as net investment hedges of foreign currency risk (notional amount in thousands): September 30, 2018 December 31, 2017 Foreign Currency Derivatives Number of Notional Amount Foreign Currency Derivatives Number of Notional Amount Sell AUD Forward 3 A$ 305,000 Sell GBP Forward 1 £ 112,700 Sell EUR Forward 1 € 185,000 Sell CAD Forward 1 C$ 95,100 Sell GBP Forward 1 £ 79,100 Sell CAD Forward 1 C$ 71,600
Summary of Outstanding Interest Rate Derivatives Designated as Cash Flow Hedges of Interest Rate Risk	The following tables detail our outstanding interest rate derivatives that were designated as cash flow hedges of interest rate risk (notional amount in thousands): September 30, 2018 Interest Rate Number of Notional Amount Strike Index Wtd.-Avg. Interest Rate Swaps 4 C$ 107,822 1.0% CDOR 0.7 Interest Rate Caps 9 $ 204,248 2.4% USD LIBOR 0.7 Interest Rate Caps 3 C$ 22,765 2.0% CDOR 0.4 December 31, 2017 Interest Rate Number of Notional Amount Strike Index Wtd.-Avg. Interest Rate Swaps 4 C$ 108,094 1.0% CDOR 1.4 Interest Rate Caps 9 $ 204,248 2.4% USD LIBOR 1.5 Interest Rate Caps 3 C$ 23,370 2.0% CDOR 0.3
Summary of Non-designated Hedges	The following tables summarize our non-designated September 30, 2018 Non-designated Number of Notional Amount Buy GBP / Sell EUR Forward 1 € 12,857 December 31, 2017 Non-designated Number of Notional Buy GBP / Sell EUR Forward 1 € 12,857
Summary of Fair Value of Derivative Financial Instruments	The following table summarizes the fair value of our derivative financial instruments ($ in thousands): Fair Value of Derivatives in an Asset Position (1) Fair Value of Derivatives in a Liability Position (2) September 30, 2018 September 30, 2018 Derivatives designated as hedging instruments: Foreign exchange contracts $ 1,514 $ — $ 3,676 $ 4,872 Interest rate derivatives 1,042 1,214 — — Total $ 2,556 $ 1,214 $ 3,676 $ 4,872 Derivatives not designated as hedging instruments: Foreign exchange contracts $ 163 $ — $ — $ 39 Interest rate derivatives — — — — Total $ 163 $ — $ — $ 39 Total Derivatives $ 2,719 $ 1,214 $ 3,676 $ 4,911 (1) Included in other assets in our consolidated balance sheets. (2) Included in other liabilities in our consolidated balance sheets.
Summary of Effect of Derivative Financial Instruments on Consolidated Statements of Operations	The following table presents the effect of our derivative financial instruments on our consolidated statements of operations ($ in thousands): Amount of Gain (Loss) Recognized in OCI on Derivatives Location of Amount of Gain (Loss) Reclassified from Accumulated OCI into Income Derivatives in Hedging Relationships Three Months Nine Months Gain (Loss) OCI into Income Three Months Nine Months Net Investment Hedges Foreign exchange contracts (1) $ 1,763 $ 23,782 Interest Expense $ — $ — Cash Flow Hedges Interest rate derivatives 92 228 Interest Expense (2) 152 388 Total $ 1,855 $ 24,011 $ 152 $ 388 (1) During the three and nine months ended September 30, 2018, we received net cash settlements of $7.6 million and $21.0 million, respectively, on our foreign currency forward contracts. Those amounts are included as a component of accumulated other comprehensive loss on our consolidated balance sheets. (2) During the three months ended September 30, 2018, we recorded total interest and related expenses of $98.0 million, which included a $152,000 expense reduction related to income generated by our cash flow hedges. During the nine months ended September 30, 2018, we recorded total interest and related expenses of $255.7 million, which included a $388,000 expense reduction related to income generated by our cash flow hedges.

Equity (Tables)

Equity (Tables)	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Summary of Class A Common Stock Issuances	The following table details our issuance of class A common stock during the nine months ended September 30, 2018 ($ in thousands, except share and per share data): Class A Common Stock Offerings 2018 Total / August 2018 At-the-Market 2018 (1) Shares issued 6,900,000 4,583,135 11,483,135 Share issue price (2) $ 32.60 $ 32.73 $ 32.65 Net proceeds (3) $ 222,275 $ 147,512 $ 369,787 (1) Issuance represents shares issued under our at-the-market (2) Represents price per share paid by the underwriters or sales agents, as applicable. Net proceeds after underwriting or sales discounts and commissions were $32.26 and $32.24 per share for our August offering and at-the-market (3) Net proceeds represents proceeds received from the underwriters less applicable transaction costs.
Schedule of Movement in Outstanding Shares of Class A Common Stock, Restricted Class A Common Stock and Deferred Stock Units	The following table details the movement in our outstanding shares of class A common stock, including restricted class A common stock and deferred stock units: Nine Months Ended September 30, Common Stock Outstanding (1) 2018 2017 Beginning balance 108,081,077 94,709,290 Issuance of class A common stock (2) 11,484,414 971 Issuance of restricted class A common stock, net 300,921 286,773 Issuance of deferred stock units 23,730 20,560 Ending balance 119,890,142 95,017,594 (1) Includes deferred stock units held by members of our board of directors of 220,947 and 189,587 as of September 30, 2018 and 2017, respectively. (2) Includes 1,279 and 971 shares issued under our dividend reinvestment program during the nine months ended September 30, 2018 and 2017, respectively.
Schedule of Dividend Activity	The following table details our dividend activity ($ in thousands, except per share data): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Dividends declared per share of common stock $ 0.62 $ 0.62 $ 1.86 $ 1.86 Total dividends declared $ 74,195 $ 58,793 $ 210,369 $ 176,374
Schedule of Basic and Diluted Earnings Per Share, or EPS, Based on Weighted-Average of Both Restricted and Unrestricted Class A Common Stock Outstanding	The following table sets forth the calculation of basic and diluted net income per share of class A common stock based on the weighted-average of both restricted and unrestricted class A common stock outstanding ($ in thousands, except per share data): Three Months Ended Nine Months Ended September 30, September 30, 2018 2017 2018 2017 Net income (1) $ 78,165 $ 57,722 $ 211,436 $ 159,741 Weighted-average shares outstanding, basic and diluted 116,203,140 95,013,087 111,251,864 95,004,188 Per share amount, basic and diluted $ 0.67 $ 0.61 $ 1.90 $ 1.68 (1) Represents net income attributable to Blackstone Mortgage Trust, Inc.

Other Expenses (Tables)

Other Expenses (Tables)	9 Months Ended
	Sep. 30, 2018
Other Income and Expenses [Abstract]
Schedule of General and Administrative Expenses	General and administrative expenses consisted of the following ($ in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Professional services (1) $ 1,022 $ 933 $ 3,383 $ 2,811 Operating and other costs (1) 687 489 2,026 1,424 Subtotal 1,709 1,422 5,409 4,235 Non-cash Restricted class A common stock earned 6,609 5,819 20,113 17,496 Director stock-based compensation 125 125 375 313 Subtotal 6,734 5,944 20,488 17,809 Total BXMT expenses 8,443 7,366 25,897 22,044 Other expenses — 53 — 175 Total general and administrative expenses $ 8,443 $ 7,419 $ 25,897 $ 22,219 (1) During the three and nine months ended September 30, 2018, we recognized an aggregate $77,000 and $302,000, respectively, of expenses related to our Multifamily Joint Venture. During both the three and nine months ended September 30, 2017, we recognized an aggregate $112,000 of expenses related to our Multifamily venture.

Stock-Based Incentive Plans (Ta

Stock-Based Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Movement in Outstanding Shares of Restricted Class A Common Stock and Weighted-Average Grant Date Fair Value Per Share	The following table details the movement in our outstanding shares of restricted class A common stock and the weighted-average grant date fair value per share: Restricted Class A Weighted-Average Balance as of December 31, 2017 1,484,175 $ 30.61 Granted 318,741 31.83 Vested (404,241 ) 28.89 Forfeited (17,820 ) 30.44 Balance as of September 30, 2018 1,380,855 $ 31.40

Fair Values (Tables)

Fair Values (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table summarizes our assets and liabilities measured at fair value on a recurring basis ($ in thousands): September 30, 2018 December 31, 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Derivatives $ — $ 2,719 $ — $ 2,719 $ — $ 1,214 $ — $ 1,214 Liabilities Derivatives $ — $ 3,676 $ — $ 3,676 $ — $ 4,911 $ — $ 4,911
Schedule of Details of Book Value, Face Amount, and Fair Value of Financial Instruments	The following table details the book value, face amount, and fair value of the financial instruments described in Note 2 ($ in thousands): September 30, 2018 December 31, 2017 Book Face Fair Book Face Fair Value Amount Value Value Amount Value Financial assets Cash and cash equivalents $ 86,987 $ 86,987 $ 86,987 $ 69,654 $ 69,654 $ 69,654 Restricted cash — — — 32,864 32,864 32,864 Loans receivable, net 12,176,516 12,260,103 12,261,013 10,056,732 10,108,226 10,112,331 Debt securities held-to-maturity (1) 96,050 99,000 97,607 — — — Financial liabilities Secured debt agreements, net 6,841,759 6,862,256 6,862,256 5,273,855 5,290,536 5,290,536 Loan participations sold, net 81,044 81,170 81,170 80,415 80,706 80,706 Securitized debt obligations, net 1,284,362 1,292,120 1,297,032 1,282,412 1,292,120 1,292,589 Convertible notes, net 780,951 794,828 832,407 563,911 575,000 610,201 (1) Included in other assets on our consolidated balance sheets.

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Assets and Liabilities of Consolidated CLO and 2017 Single Asset Securitization VIE	The following table details the assets and liabilities of our consolidated CLO and 2017 Single Asset Securitization VIEs ($ in thousands): September 30, 2018 Assets: Loans receivable, net $ 1,500,000 $ 1,500,000 Other assets 4,899 2,407 Total assets $ 1,504,899 $ 1,502,407 Liabilities: Securitized debt obligations, net $ 1,284,362 $ 1,282,412 Other liabilities 1,869 1,379 Total liabilities $ 1,286,231 $ 1,283,791

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Principal Contractual Obligations	Our contractual principal debt repayments as of September 30, 2018 were as follows ($ in thousands): Payment Timing Total Less Than 1 Year 1 to 3 Years 3 to 5 Years More Than 5 Years Principal repayments under secured debt agreements (1) $ 6,862,256 $ 273,254 $ 2,393,008 $ 4,112,794 $ 83,200 Principal repayments of convertible notes (2) 794,828 172,328 — 622,500 — Total (3) $ 7,657,084 $ 445,582 $ 2,393,008 $ 4,735,294 $ 83,200 (1) The allocation of repayments under our secured debt agreements is based on the earlier of (i) the maturity date of each facility, or (ii) the maximum maturity date of the collateral loans, assuming all extension options are exercised by the borrower. (2) Reflects the outstanding principal balance of convertible notes, excluding any potential conversion premium. Refer to Note 8 for further details on our convertible notes. (3) As of September 30, 2018, the total does not include $81.2 million of loan participations sold, $466.7 million of non-consolidated

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2018	Apr. 30, 2017	Jun. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Joint venture capital contribution percentage		85.00%
Income accrual, description	Income accrual is generally suspended for loans at the earlier of the date at which payments become 90 days past due or when, in the opinion of our Manager, recovery of income and principal becomes doubtful.
Cash and cash equivalents, description	Cash and cash equivalents represent cash held in banks and liquid investments with original maturities of three months or less.
Expected loss	$ 0
Provision for loan losses	$ 0
Walker and Dunlop [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Joint venture capital contribution percentage		15.00%
General Electrical Capital Corporation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchase price of Loan Portfolio			$ 4,700,000,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 86,987	$ 69,654	$ 61,221
Restricted cash		32,864	32,864
Total cash, cash equivalents, and restricted cash shown in our consolidated statements of cash flows	$ 86,987	$ 102,518	$ 94,085	$ 75,567

Loans Receivable, Net - Overall

Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)SecurityLoan	Dec. 31, 2017USD ($)SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	112	110
Net book value	$ 12,176,516	$ 10,056,732
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	112	110
Principal balance	$ 12,260,103	$ 10,108,226
Unfunded loan commitments	$ 3,046,350	$ 1,573,107
Weighted-average maximum maturity (years)	3 years 9 months 18 days	3 years 6 months
Loans Receivable [Member] | LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average cash coupon, rate	5.61%	5.55%
Weighted-average all-in yield, rate	5.94%	5.95%
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 12,176,516	$ 10,056,732

Loans Receivable, Net - Overa_2

Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Parenthetical) (Detail)	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans subject to yield maintenance, or other prepayment restrictions	86.00%	75.00%
Percentage of loans open to repayment by borrower without penalty	14.00%	25.00%
USD LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans receivable by type	83.00%	92.00%

Loans Receivable, Net - Activit

Loans Receivable, Net - Activity Relating to Loans Receivable Portfolio (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance			$ 10,056,732
Loan contributed to securitization	$ 517,500
Unrealized (loss) gain on foreign currency translation	(2,416)	$ 16,175	(26,766)	$ 43,990
Amortization of fees and other items			35,955	$ 28,887
Ending Balance	12,176,516		12,176,516
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance			10,056,732
Loan fundings			5,222,803
Loan repayments			(2,452,811)
Loan contributed to securitization			512,002
Unrealized (loss) gain on foreign currency translation			(99,937)
Deferred fees and other items			(74,111)
Amortization of fees and other items			35,842
Ending Balance	12,176,516		12,176,516
Deferred Fees/Other Items [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance			(51,494)
Loan contributed to securitization			5,498
Unrealized (loss) gain on foreign currency translation			678
Deferred fees and other items			(74,111)
Amortization of fees and other items			35,842
Ending Balance	(83,587)		(83,587)
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning Balance			10,108,226
Loan fundings			5,222,803
Loan repayments			(2,452,811)
Loan contributed to securitization			517,500
Unrealized (loss) gain on foreign currency translation			(100,615)
Ending Balance	$ 12,260,103		$ 12,260,103

Loans Receivable, Net - Propert

Loans Receivable, Net - Property Type and Geographic Distribution of Properties Securing Loans in Portfolio (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)SecurityLoan	Dec. 31, 2017USD ($)SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	112	110
Net book value	$ 12,176,516	$ 10,056,732
Total Loan Exposure	$ 12,726,831	$ 11,093,608
Percentage of Portfolio	100.00%	100.00%
Office [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	49	53
Net book value	$ 5,956,675	$ 5,773,972
Total Loan Exposure	$ 6,006,534	$ 5,807,170
Percentage of Portfolio	47.00%	53.00%
Hotel [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	15	15
Net book value	$ 1,992,889	$ 1,830,568
Total Loan Exposure	$ 2,069,818	$ 1,905,497
Percentage of Portfolio	16.00%	17.00%
Multifamily [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	32	6
Net book value	$ 1,894,001	$ 487,473
Total Loan Exposure	$ 1,903,572	$ 940,980
Percentage of Portfolio	15.00%	8.00%
Spanish Assets [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	1
Net book value	$ 1,152,487
Total Loan Exposure	$ 1,160,400
Percentage of Portfolio	9.00%
Retail [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	4	25
Net book value	$ 336,787	$ 1,220,423
Total Loan Exposure	$ 337,334	$ 1,228,959
Percentage of Portfolio	3.00%	11.00%
Condominium [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	2	2
Net book value	$ 84,429	$ 142,342
Total Loan Exposure	$ 158,462	$ 268,751
Percentage of Portfolio	1.00%	2.00%
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	9	9
Net book value	$ 759,248	$ 601,954
Total Loan Exposure	$ 1,090,711	$ 942,251
Percentage of Portfolio	9.00%	9.00%
United States Northeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	30	26
Net book value	$ 3,796,633	$ 2,857,948
Total Loan Exposure	$ 3,830,021	$ 2,871,219
Percentage of Portfolio	29.00%	26.00%
United States West [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	25	29
Net book value	$ 2,543,743	$ 2,672,069
Total Loan Exposure	$ 2,637,582	$ 2,816,276
Percentage of Portfolio	21.00%	24.00%
United States Southeast [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	18	17
Net book value	$ 2,025,381	$ 2,007,202
Total Loan Exposure	$ 2,034,852	$ 2,470,992
Percentage of Portfolio	16.00%	22.00%
United States Midwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	8	9
Net book value	$ 901,310	$ 856,559
Total Loan Exposure	$ 906,102	$ 862,578
Percentage of Portfolio	7.00%	8.00%
United States Southwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	13	10
Net book value	$ 477,809	$ 380,204
Total Loan Exposure	$ 480,792	$ 380,120
Percentage of Portfolio	4.00%	3.00%
United States Northwest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	2	2
Net book value	$ 141,199	$ 283,381
Total Loan Exposure	$ 141,630	$ 286,221
Percentage of Portfolio	1.00%	3.00%
United States [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	96	93
Net book value	$ 9,886,075	$ 9,057,363
Total Loan Exposure	$ 10,030,979	$ 9,687,406
Percentage of Portfolio	78.00%	86.00%
Spain [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	1
Net book value	$ 1,152,487
Total Loan Exposure	$ 1,160,400
Percentage of Portfolio	9.00%
United Kingdom [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	5	6
Net book value	$ 492,790	$ 440,317
Total Loan Exposure	$ 837,688	$ 794,789
Percentage of Portfolio	7.00%	7.00%
Canada [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	5	7
Net book value	$ 335,957	$ 415,893
Total Loan Exposure	$ 332,841	$ 412,343
Percentage of Portfolio	3.00%	4.00%
Australia [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	2
Net book value	$ 218,286
Total Loan Exposure	$ 220,335
Percentage of Portfolio	2.00%
Belgium [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	1	1
Net book value	$ 71,494	$ 73,779
Total Loan Exposure	$ 71,945	$ 74,431
Percentage of Portfolio	1.00%	1.00%
Germany [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	1	1
Net book value	$ 11,814	$ 12,237
Total Loan Exposure	$ 65,000	$ 67,399
Percentage of Portfolio		1.00%
Netherlands [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	1	2
Net book value	$ 7,613	$ 57,143
Total Loan Exposure	$ 7,643	$ 57,240
Percentage of Portfolio		1.00%
International [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	16	17
Net book value	$ 2,290,441	$ 999,369
Total Loan Exposure	$ 2,695,852	$ 1,406,202
Percentage of Portfolio	22.00%	14.00%

Loans Receivable, Net - Prope_2

Loans Receivable, Net - Property Type and Geographic Distribution of Properties Securing Loans in Portfolio (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Jul. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan exposure including senior interests	$ 466.7		$ 985.4
Single asset securitization principal amount		$ 1,000		$ 474.6
2018 Single Asset Securitization [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Single asset securitization principal amount	$ 1,000

Loans Receivable, Net - Princip

Loans Receivable, Net - Principal Balance and Net Book Value of Loans Receivable Based on Internal Risk Ratings (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)SecurityLoan	Dec. 31, 2017USD ($)SecurityLoan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	112	110
Net book value	$ 12,176,516	$ 10,056,732
Total Loan Exposure	$ 12,726,831	$ 11,093,608
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	112	110
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 12,176,516	$ 10,056,732
Risk Rating 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loan Exposure	$ 53,873	$ 31,890
Risk Rating 1 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	1	1
Risk Rating 1 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 53,849	$ 31,842
Risk Rating 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loan Exposure	$ 4,272,068	$ 3,521,701
Risk Rating 2 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	43	41
Risk Rating 2 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 4,167,871	$ 3,512,709
Risk Rating 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loan Exposure	$ 8,400,890	$ 7,519,465
Risk Rating 3 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	68	67
Risk Rating 3 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 7,954,796	$ 6,491,617
Risk Rating 4 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loan Exposure		$ 20,552
Risk Rating 4 [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan		1
Risk Rating 4 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value		$ 20,564

Loans Receivable, Net - Princ_2

Loans Receivable, Net - Principal Balance and Net Book Value of Loans Receivable Based on Internal Risk Ratings (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Jul. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loan exposure including senior interests	$ 466.7		$ 985.4
Single asset securitization principal amount		$ 1,000		$ 474.6
2018 Single Asset Securitization [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Single asset securitization principal amount	$ 1,000

Loans Receivable, Net - Additio

Loans Receivable, Net - Additional Information (Detail)	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average risk rating on loan exposure	2.7	2.7
Impaired loans	$ 0	$ 0
Loans held	12,726,831,000	11,093,608,000
Multifamily [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held	1,903,572,000	940,980,000
Joint Venture [Member] | Multifamily [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held	$ 222,700,000	$ 182,200,000

Other Assets and Liabilities -

Other Assets and Liabilities - Summary of Components of Other Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Debt securities held-to-maturity	$ 96,050
Accrued interest receivable	45,762	$ 38,573
Collateral deposited under derivative agreements	7,360	4,120
Loan portfolio payments held by servicer	3,902	54,759
Derivative assets	2,719	1,214
Prepaid expenses	151	798
Prepaid taxes	28	31
Other		80
Total	$ 155,972	$ 99,575

Other Assets and Liabilities _2

Other Assets and Liabilities - Summary of Components of Other Assets (Parenthetical) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Jul. 31, 2018	Jun. 30, 2017
Schedule Of Other Assets [Line Items]
Subordinate risk retention interest	$ 99
Percentage of yield in subordinate risk retention interest	10.00%
Single asset securitization principal amount		$ 1,000	$ 474.6
2018 Single Asset Securitization [Member]
Schedule Of Other Assets [Line Items]
Single asset securitization principal amount	$ 1,000
Single asset securitization maximum maturity date	Jun. 9, 2025

Other Assets and Liabilities _3

Other Assets and Liabilities - Summary of Components of Other Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Liabilities [Abstract]
Accrued dividends payable	$ 74,195	$ 66,888
Accrued interest payable	23,701	14,162
Accrued management and incentive fees payable	18,368	14,284
Derivative liabilities	3,676	4,911
Accounts payable and other liabilities	3,426	2,125
Secured debt repayments pending servicer remittance		38,456
Total	$ 123,366	$ 140,826

Secured Debt Agreements, Net -

Secured Debt Agreements, Net - Schedule of Secured Debt Agreements (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Secured debt agreements borrowings outstanding	$ 6,862,256	$ 5,290,536
Deferred financing costs	(20,497)	(16,681)
Net book value of secured debt	6,841,759	5,273,855
Credit Facilities [Member]
Debt Instrument [Line Items]
Secured debt agreements borrowings outstanding	4,850,911	4,068,249
GE Portfolio Acquisition Facility [Member]
Debt Instrument [Line Items]
Secured debt agreements borrowings outstanding	512,059	703,423
Asset-Specific Financings [Member]
Debt Instrument [Line Items]
Secured debt agreements borrowings outstanding	$ 1,499,286	$ 518,864

Secured Debt Agreements, Net _2

Secured Debt Agreements, Net - Additional Information (Detail) € in Millions	3 Months Ended		9 Months Ended				12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Facility	Sep. 30, 2018GBP (£)Facility	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2018EUR (€)	Sep. 30, 2018GBP (£)	Dec. 31, 2017GBP (£)
Debt Instrument [Line Items]
Aggregate borrowings	$ 5,409,815,000		$ 5,409,815,000
Basis spread on debt obligation, in percent			1.77%	1.77%
Weighted-average advance rate			79.20%	79.20%
Secured debt agreements borrowings outstanding					$ 38,456,000		$ 38,456,000
Maximum Facility Size	651,600,000		$ 651,600,000		675,700,000		675,700,000		£ 500,000,000	£ 500,000,000
Interest expense	97,955,000	$ 67,891,000	255,677,000			$ 168,917,000
Secured debt agreements borrowings outstanding	6,862,256,000		6,862,256,000		5,290,536,000		5,290,536,000
Covenants, minimum tangible net worth	$ 2,400,000,000		$ 2,400,000,000
Covenants, percentage of tangible assets on cash proceeds from equity issuances			75.00%	75.00%
Covenants, percentage of recourse indebtedness	5.00%		5.00%					5.00%	5.00%
Maximum [Member]
Debt Instrument [Line Items]
Covenants, indebtedness to total assets, in percent	83.33%		83.33%					83.33%	83.33%
Minimum [Member]
Debt Instrument [Line Items]
Covenants, EBITDA to fixed charges, in percent			140.00%	140.00%
Covenants, minimum cash liquidity amount	$ 10,000,000		$ 10,000,000
Asset-Specific Financings [Member]
Debt Instrument [Line Items]
Weighted-average outstanding balance			1,300,000,000		522,500,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Weighted-average outstanding balance			37,800,000		40,700,000
Interest expense			2,600,000		2,600,000
Amortization of deferred fees and expenses			825,000		703,000
Secured debt agreements borrowings outstanding	0		0		0		0
Revolving Credit Facility [Member] | Barclays [Member]
Debt Instrument [Line Items]
Maximum Facility Size	250,000,000		$ 250,000,000
First mortgage bridge to term financing maximum period			6 months	6 months
Credit Facilities [Member]
Debt Instrument [Line Items]
Additional credit capacity | £				£ 250,000,000
Weighted-average outstanding balance			$ 4,400,000,000		4,200,000,000
Aggregate borrowings	4,850,911,000		$ 4,850,911,000		4,068,249,000		$ 4,068,249,000
Weighted-average advance rate			79.20%	79.20%			78.70%
Weighted-average initial maturity			1 year 6 months	1 year 6 months			1 year 6 months
Maximum Facility Size	8,315,710,000		$ 8,315,710,000		7,155,975,000		$ 7,155,975,000
Secured debt agreements borrowings outstanding	4,850,911,000		4,850,911,000		$ 4,068,249,000		$ 4,068,249,000
Credit Facilities [Member] | Barclays [Member]
Debt Instrument [Line Items]
Aggregate borrowings	617,360,000		617,360,000
Maximum Facility Size	$ 1,000,000,000		$ 1,000,000,000
New Credit Facilities [Member]
Debt Instrument [Line Items]
Number of new credit facility | Facility			1	1
Additional credit capacity | £				£ 1,000,000,000
Asset-Specific Financings [Member]
Debt Instrument [Line Items]
Secured debt agreements borrowings outstanding | €								€ 800
Asset-Specific Financings [Member] | Senior Loan [Member]
Debt Instrument [Line Items]
Secured loan | €								€ 1,000
LIBOR [Member] | Credit Facilities [Member] | Weighted-Average Cash Coupon [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent			1.77%	1.77%			1.90%
LIBOR [Member] | Credit Facilities [Member] | Weighted-Average All-in Cost of Credit [Member]
Debt Instrument [Line Items]
Basis spread on debt obligation, in percent			1.98%	1.98%			2.12%

Secured Debt Agreements, Net _3

Secured Debt Agreements, Net - Credit Facilities (Detail)	Sep. 30, 2018USD ($)	Sep. 30, 2018EUR (€)	Sep. 30, 2018GBP (£)	Dec. 31, 2017USD ($)	Dec. 31, 2017EUR (€)	Dec. 31, 2017GBP (£)
Line of Credit Facility [Line Items]
Maximum Facility Size	$ 651,600,000		£ 500,000,000	$ 675,700,000		£ 500,000,000
Potential	4,850,911,000
Repurchase Borrowings Outstanding	5,409,815,000
Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	8,315,710,000			7,155,975,000
Potential	5,409,814,000			4,664,097,000
Repurchase Borrowings Outstanding	4,850,911,000			4,068,249,000
Available	558,903,000			595,848,000
Collateral Assets	7,046,983,000			6,064,983,000
Bank of America [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	1,000,000,000			750,000,000
Potential	863,592,000			573,542,000
Repurchase Borrowings Outstanding	863,592,000			573,542,000
Collateral Assets	1,091,860,000			765,049,000
Wells Fargo [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	2,000,000,000			2,000,000,000
Potential	1,160,678,000			1,289,135,000
Repurchase Borrowings Outstanding	850,687,000			1,170,801,000
Available	309,991,000			118,334,000
Collateral Assets	1,577,251,000			1,680,325,000
MetLife [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	1,000,000,000			1,000,000,000
Potential	737,770,000			807,164,000
Repurchase Borrowings Outstanding	737,770,000			807,164,000
Collateral Assets	946,933,000			1,039,231,000
Barclays [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	1,000,000,000
Potential	617,360,000
Repurchase Borrowings Outstanding	617,360,000
Collateral Assets	771,700,000
Citibank [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	750,000,000			800,125,000
Potential	576,369,000			354,354,000
Repurchase Borrowings Outstanding	480,129,000			240,881,000
Available	96,240,000			113,473,000
Collateral Assets	730,723,000			455,433,000
JP Morgan [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	500,000,000			500,000,000
Potential	435,095,000			443,496,000
Repurchase Borrowings Outstanding	332,909,000			319,755,000
Available	102,186,000			123,741,000
Collateral Assets	564,070,000			579,218,000
Morgan Stanley [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	651,550,000			675,650,000
Potential	329,256,000			456,344,000
Repurchase Borrowings Outstanding	278,770,000			216,044,000
Available	50,486,000			240,300,000
Collateral Assets	461,760,000			591,168,000
Deutsche Bank [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	500,000,000			500,000,000
Potential	277,247,000			295,743,000
Repurchase Borrowings Outstanding	277,247,000			295,743,000
Collateral Assets	380,986,000			399,203,000
Societe Generale [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	464,160,000	€ 400		480,200,000	€ 400
Potential	235,229,000			300,871,000
Repurchase Borrowings Outstanding	235,229,000			300,871,000
Collateral Assets	298,951,000			373,181,000
Goldman Sachs - Multi. JV [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	250,000,000			250,000,000
Potential	117,498,000			57,888,000
Repurchase Borrowings Outstanding	117,498,000			57,888,000
Collateral Assets	148,099,000			75,225,000
Bank of America - Multi. JV [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	200,000,000			200,000,000
Potential	59,720,000			85,560,000
Repurchase Borrowings Outstanding	59,720,000			85,560,000
Collateral Assets	$ 74,650,000			$ 106,950,000

Secured Debt Agreements, Net _4

Secured Debt Agreements, Net - Credit Facilities (Parenthetical) (Detail)	Sep. 30, 2018USD ($)	Sep. 30, 2018EUR (€)	Sep. 30, 2018GBP (£)	Dec. 31, 2017USD ($)	Dec. 31, 2017EUR (€)	Dec. 31, 2017GBP (£)
Line of Credit Facility [Line Items]
Maximum Facility Size	$ 651,600,000		£ 500,000,000	$ 675,700,000		£ 500,000,000
Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	8,315,710,000			7,155,975,000
Citibank [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	750,000,000			800,125,000
Citibank [Member] | Credit Facilities [Member] | UK Pound Sterling 250.0 Million ($300.0 Million) Facility [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size				300,100,000	€ 250,000,000
Citibank [Member] | Credit Facilities [Member] | $500.0 Million Facility [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size				500,000,000
Societe Generale [Member] | Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Facility Size	$ 464,160,000	€ 400		$ 480,200,000	€ 400

Secured Debt Agreements, Net _5

Secured Debt Agreements, Net - Summary of Key Terms of Credit Facilities (Detail) € in Thousands, £ in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2018EUR (€)	Sep. 30, 2018GBP (£)
Line of Credit Facility [Line Items]
Outstanding Borrowings	$ 5,409,815
Potential Borrowings	$ 4,850,911
Rate	1.77%
Advance Rate	79.20%
Credit Facilities [Member]
Line of Credit Facility [Line Items]
Outstanding Borrowings	$ 4,850,911	$ 4,068,249
Potential Borrowings	$ 5,409,814	$ 4,664,097
Advance Rate	79.20%	78.70%
Credit Facilities [Member] | 1-Month USD LIBOR [Member]
Line of Credit Facility [Line Items]
Outstanding Borrowings	$ 5,024,025
Potential Borrowings	$ 4,551,603
Rate	1.75%
Advance Rate	79.20%
Credit Facilities [Member] | 3-Month EUR LIBOR [Member]
Line of Credit Facility [Line Items]
Outstanding Borrowings | €			€ 54,869
Potential Borrowings | €			€ 12,100
Rate	2.28%
Advance Rate	80.00%
Credit Facilities [Member] | 3-Month GBP LIBOR [Member]
Line of Credit Facility [Line Items]
Outstanding Borrowings | £				£ 247,194
Potential Borrowings | £				£ 218,914
Rate	1.97%
Advance Rate	79.00%
Credit Facilities [Member] | Wells Fargo [Member]
Line of Credit Facility [Line Items]
Guarantee	25.00%
Margin Call	Collateral marks only
Term/Maturity	Term matched
Outstanding Borrowings	$ 850,687	$ 1,170,801
Potential Borrowings	$ 1,160,678	1,289,135
Credit Facilities [Member] | MetLife [Member]
Line of Credit Facility [Line Items]
Guarantee	50.00%
Margin Call	Collateral marks only
Term/Maturity	Apr. 22, 2023
Outstanding Borrowings	$ 737,770	807,164
Potential Borrowings	$ 737,770	807,164
Credit Facilities [Member] | Bank of America [Member]
Line of Credit Facility [Line Items]
Guarantee	50.00%
Margin Call	Collateral marks only
Term/Maturity	May 21, 2023
Outstanding Borrowings	$ 863,592	573,542
Potential Borrowings	$ 863,592	573,542
Credit Facilities [Member] | Societe Generale [Member]
Line of Credit Facility [Line Items]
Guarantee	25.00%
Margin Call	Collateral marks only
Term/Maturity	Term matched
Outstanding Borrowings	$ 235,229	300,871
Potential Borrowings	$ 235,229	300,871
Credit Facilities [Member] | Deutsche Bank [Member]
Line of Credit Facility [Line Items]
Guarantee	32.00%
Margin Call	Collateral marks only
Term/Maturity	Aug. 9, 2021
Outstanding Borrowings	$ 277,247	295,743
Potential Borrowings	$ 277,247	295,743
Credit Facilities [Member] | Citibank [Member]
Line of Credit Facility [Line Items]
Guarantee	25.00%
Margin Call	Collateral marks only
Term/Maturity	Term matched
Outstanding Borrowings	$ 480,129	240,881
Potential Borrowings	$ 576,369	354,354
Credit Facilities [Member] | Morgan Stanley [Member]
Line of Credit Facility [Line Items]
Guarantee	25.00%
Margin Call	Collateral marks only
Term/Maturity	Mar. 3, 2020
Outstanding Borrowings	$ 278,770	216,044
Potential Borrowings	$ 329,256	456,344
Credit Facilities [Member] | JP Morgan [Member]
Line of Credit Facility [Line Items]
Guarantee	50.00%
Margin Call	Collateral marks only
Term/Maturity	Jan. 7, 2021
Outstanding Borrowings	$ 332,909	319,755
Potential Borrowings	$ 435,095	443,496
Credit Facilities [Member] | Bank of America - Multi. JV [Member]
Line of Credit Facility [Line Items]
Guarantee	43.00%
Margin Call	Collateral marks only
Term/Maturity	Jul. 19, 2021
Outstanding Borrowings	$ 59,720	85,560
Potential Borrowings	$ 59,720	85,560
Credit Facilities [Member] | Goldman Sachs - Multi. JV [Member]
Line of Credit Facility [Line Items]
Guarantee	25.00%
Margin Call	Collateral marks only
Term/Maturity	Jul. 12, 2020
Outstanding Borrowings	$ 117,498	57,888
Potential Borrowings	$ 117,498	$ 57,888
Credit Facilities [Member] | Barclays [Member]
Line of Credit Facility [Line Items]
Guarantee	25.00%
Margin Call	Collateral marks only
Term/Maturity	Mar. 29, 2023
Outstanding Borrowings	$ 617,360
Potential Borrowings	$ 617,360

Secured Debt Agreements, Net _6

Secured Debt Agreements, Net - Summary of Key Terms of Credit Facilities (Parenthetical) (Detail) - Credit Facilities [Member]	9 Months Ended
	Sep. 30, 2018ExtensionOptions
MetLife [Member]
Line of Credit Facility [Line Items]
Maturity period	Includes four one-year extension options which may be exercised at our sole discretion.
Number of extension options	4
Term of maturity date	1 year
Number of extension options	4
Term of maturity date	1 year
Maturity period	Includes four one-year extension options which may be exercised at our sole discretion.
Bank of America [Member]
Line of Credit Facility [Line Items]
Maturity period	Includes two one-year extension options which may be exercised at our sole discretion.
Number of extension options	2
Term of maturity date	1 year
Number of extension options	2
Term of maturity date	1 year
Maturity period	Includes two one-year extension options which may be exercised at our sole discretion.
Deutsche Bank [Member]
Line of Credit Facility [Line Items]
Maturity period	Includes two one-year extension options which may be exercised at our sole discretion.
Number of extension options	2
Term of maturity date	1 year
Number of extension options	2
Term of maturity date	1 year
Maturity period	Includes two one-year extension options which may be exercised at our sole discretion.
Goldman Sachs - Multi. JV [Member]
Line of Credit Facility [Line Items]
Maturity period	Includes one one-year extension option which may be exercised at our sole discretion.
Number of extension options	1
Term of maturity date	1 year
Number of extension options	1
Term of maturity date	1 year
Maturity period	Includes one one-year extension option which may be exercised at our sole discretion.
Barclays [Member]
Line of Credit Facility [Line Items]
Maturity period	Includes four one-year extension options which may be exercised at our sole discretion.
Number of extension options	4
Term of maturity date	1 year
Number of extension options	4
Term of maturity date	1 year
Maturity period	Includes four one-year extension options which may be exercised at our sole discretion.

Secured Debt Agreements, Net _7

Secured Debt Agreements, Net - Summary of Asset-Specific Financings (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)SecurityLoan	Dec. 31, 2017USD ($)SecurityLoan
GE Portfolio Acquisition Facility [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2021-05	2020-07
Guarantee	$ 250,000	$ 250,000
Collateral assets, Book Value	664,189	911,092
Financing provided, Book Value	511,346	702,337
Collateral assets, Principal Balance	662,464	906,707
Financing provided, Principal Balance	$ 512,059	$ 703,423
Count | SecurityLoan	11	16
GE Portfolio Acquisition Facility [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2021-05	2020-07
Count | SecurityLoan	11	16
GE Portfolio Acquisition Facility [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	1.77%	1.72%
GE Portfolio Acquisition Facility [Member] | LIBOR [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	5.92%	5.74%
Asset-Specific Financings [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2022-09	2020-12
Guarantee	$ 1,178,874	$ 162,475
Collateral assets, Book Value	1,895,094	677,296
Financing provided, Book Value	1,492,614	517,088
Collateral assets, Principal Balance	1,905,475	682,259
Financing provided, Principal Balance	$ 1,499,286	$ 518,864
Count | SecurityLoan	5	6
Asset-Specific Financings [Member] | Collateral Assets [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Term	2022-09	2020-12
Count | SecurityLoan	5	6
Asset-Specific Financings [Member] | LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost Rate	1178874.00%	162475.00%

Secured Debt Agreements, Net _8

Secured Debt Agreements, Net - Summary of Asset-Specific Financings (Parenthetical) (Detail)	9 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2018GBP (£)	Dec. 31, 2017USD ($)	Dec. 31, 2017GBP (£)
Participating Mortgage Loans [Line Items]
Maximum Facility Size	$ 651,600,000	£ 500,000,000	$ 675,700,000	£ 500,000,000
Approximate credit line, outstanding amount	5,409,815,000
GE Portfolio Acquisition Facility [Member]
Participating Mortgage Loans [Line Items]
Borrowings	512,059,000		703,423,000
Maximum Facility Size	608,700,000		816,300,000
Approximate credit line, outstanding amount	512,100,000		703,400,000
Amount available for potential future fundings of loan	$ 96,600,000		112,900,000
GE Portfolio Acquisition Facility [Member] | Maximum [Member]
Participating Mortgage Loans [Line Items]
Percentage of guarantee rate	25.00%	25.00%
Guarantee of outstanding borrowings	$ 250,000,000
Asset-Specific Financings [Member]
Participating Mortgage Loans [Line Items]
Borrowings	1,499,286,000		518,864,000
Cross Collateral Assets [Member] | Asset-Specific Financings [Member]
Participating Mortgage Loans [Line Items]
Borrowings	$ 517,800,000		$ 394,800,000

Loan Participations Sold, Net -

Loan Participations Sold, Net - Summary of Statistics for Loan Participations Sold (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)SecurityLoan	Dec. 31, 2017USD ($)LoansSecurityLoan
Participating Mortgage Loans [Line Items]
Count | SecurityLoan	1	1
Principal Balance	$ 106,259	$ 141,119
Weighted Average Term	2022-02	2022-02
Book Value, Total Loan	$ 12,176,516	$ 10,056,732
Book Value	$ 81,044	$ 80,415
Senior Participation [Member]
Participating Mortgage Loans [Line Items]
Count	1	1
Principal Balance	$ 81,170	$ 80,706
Weighted Average Term	2022-02	2022-02
Book Value	$ 81,044	$ 80,415
Loan Participations Sold [Member]
Participating Mortgage Loans [Line Items]
Book Value, Total Loan	$ 105,149	$ 138,907
LIBOR [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost	6.06%	5.94%
LIBOR [Member] | Senior Participation [Member]
Participating Mortgage Loans [Line Items]
Weighted Average Yield/Cost	4.08%	4.14%

Loan Participations Sold, Net_2

Loan Participations Sold, Net - Summary of Statistics for Loan Participations Sold (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Participating Mortgage Loans [Line Items]
Deferred financing costs	$ 20,497		$ 20,497		$ 16,681
Loan Participations Sold [Member]
Participating Mortgage Loans [Line Items]
Interest expense	11,700	$ 4,000	15,200	$ 9,300
Deferred financing costs	$ 126,000		$ 126,000		$ 291,000

Securitized Debt Obligations,_3

Securitized Debt Obligations, Net - Schedule of Information on Securitized Debt Obligations (Detail) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)Loans	Dec. 31, 2017USD ($)Loans	Jul. 31, 2018USD ($)	Jun. 30, 2017USD ($)
Debt Instrument [Line Items]
Principal Balance			$ 1,000,000	$ 474,600
Financing Provided [Member]
Debt Instrument [Line Items]
Count | Loans	2	2
Principal Balance	$ 1,292,120	$ 1,292,120
Book Value	$ 1,284,362	$ 1,282,411
Financing Provided [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Wtd. Avg. Yield/Cost	1.71%	1.83%
Financing Provided [Member] | 2017 Single Asset Securitization [Member]
Debt Instrument [Line Items]
Count | Loans	1	1
Principal Balance	$ 474,620	$ 474,620
Book Value	$ 474,418	$ 474,328
Term	2033-06	2033-06
Financing Provided [Member] | 2017 Single Asset Securitization [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Wtd. Avg. Yield/Cost	1.65%	1.94%
Financing Provided [Member] | Collateralized Loan Obligations [Member]
Debt Instrument [Line Items]
Count | Loans	1	1
Principal Balance	$ 817,500	$ 817,500
Book Value	$ 809,944	$ 808,083
Term	2035-06	2035-06
Financing Provided [Member] | Collateralized Loan Obligations [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Wtd. Avg. Yield/Cost	1.74%	1.76%
Collateral Assets [Member]
Debt Instrument [Line Items]
Count | Loans	29	32
Principal Balance	$ 1,678,963	$ 1,656,406
Book Value	$ 1,675,437	$ 1,652,880
Wtd. Avg. Yield/Cost	6.00%	5.17%
Collateral Assets [Member] | 2017 Single Asset Securitization [Member]
Debt Instrument [Line Items]
Count | Loans	1	1
Principal Balance	$ 678,963	$ 656,406
Book Value	$ 675,437	$ 652,880
Term	2023-06	2023-06
Collateral Assets [Member] | 2017 Single Asset Securitization [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Wtd. Avg. Yield/Cost	3.60%	3.60%
Collateral Assets [Member] | Collateralized Loan Obligations [Member]
Debt Instrument [Line Items]
Count | Loans	28	31
Principal Balance	$ 1,000,000	$ 1,000,000
Book Value	$ 1,000,000	$ 1,000,000
Wtd. Avg. Yield/Cost	6.09%	5.16%
Term	2022-02	2021-11

Securitized Debt Obligations,_4

Securitized Debt Obligations, Net - Schedule of Information on Securitized Debt Obligations (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Percentage of loans financed by securitized debt obligations earned floating rate of interest			98.00%		98.00%
Interest expense on securitized debt obligations	$ 12.5	$ 3.8	$ 35.6	$ 3.8
Collateral Assets [Member] | 2017 Single Asset Securitization [Member]
Debt Instrument [Line Items]
Total loan amount, securitized	$ 500		$ 500

Convertible Notes, Net - Summar

Convertible Notes, Net - Summary of Outstanding Convertible Senior Notes (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)
5.25% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Note Issuance	2013-11
Face Value	$ 172,328
Coupon Rate	5.25%
All-in Cost	5.87%
Conversion Rate	36.5472
Maturity	Dec. 1, 2018
4.38% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Note Issuance	2017-05
Face Value	$ 402,500
Coupon Rate	4.38%
All-in Cost	4.85%
Conversion Rate	28.0324
Maturity	May 5, 2022
4.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Note Issuance	2018-03
Face Value	$ 220,000
Coupon Rate	4.75%
All-in Cost	5.33%
Conversion Rate	27.6052
Maturity	Mar. 15, 2023

Convertible Notes, Net - Summ_2

Convertible Notes, Net - Summary of Outstanding Convertible Senior Notes (Parenthetical) (Detail)	Oct. 15, 2018	Jul. 16, 2018	Mar. 28, 2018USD ($)$ / shares	Sep. 30, 2018USD ($)$ / shares	Sep. 28, 2018$ / shares
5.25% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price					$ 33.51
Convertible Notes, debt conversion, common stock issued, in percent				36.5472
5.25% Convertible Senior Notes [Member] | Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, principal amount | $				$ 1,000
4.38% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, common stock issued, in percent				28.0324
4.38% Convertible Senior Notes [Member] | Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, principal amount | $				$ 1,000
Convertible Senior Notes [Member] | Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, principal amount | $			$ 1,000
Debt instrument, conversion price			$ 27.67
Convertible Notes, debt conversion, common stock issued, in percent		36.8161	36.1380
Convertible Senior Notes [Member] | Class A Common Stock [Member] | Subsequent Events [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, common stock issued, in percent	36.8161
5.25% Convertible Senior Notes Issued in November 2013 [Member] | Class A Common Stock [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price				$ 27.36
4.38% Convertible Senior Notes Issued in May 2017 [Member] | Class A Common Stock [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price				$ 35.67
4.75% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, common stock issued, in percent				27.6052
4.75% Convertible Senior Notes [Member] | Class A Common Stock [Member]
Debt Instrument [Line Items]
Convertible Notes, debt conversion, principal amount | $				$ 1,000
4.75% Convertible Senior Notes Issued In March 2018 [Member] | Class A Common Stock [Member]
Debt Instrument [Line Items]
Debt instrument, conversion price				$ 36.23

Convertible Notes, Net - Additi

Convertible Notes, Net - Additional Information (Detail) - USD ($)	1 Months Ended	9 Months Ended
	Mar. 31, 2018	Sep. 30, 2018	Sep. 28, 2018	Dec. 31, 2017	May 31, 2017	Nov. 30, 2013
Debt Instrument [Line Items]
Accrued interest payable		$ 23,701,000		$ 14,162,000
5.25% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Description of Convertible Notes conversion		The Convertible Notes are convertible at the holders' option into shares of our class A common stock, only under specific circumstances, prior to the close of business on August 31, 2018, January 31, 2022, and December 14, 2022 for the November 2013, May 2017, and March 2018 convertible notes, respectively, at the applicable conversion rate in effect on the conversion date.
Debt instrument, conversion price			$ 33.51
Discount upon issuance of Convertible Notes						$ 9,100,000
Debt issuance costs						$ 4,100,000
Convertible Notes, assumed effective interest rate						6.50%
Convertible Senior Notes, Interest rate including amortization of discount upon issuance						7.16%
Accrued interest payable		$ 10,800,000		$ 3,700,000
4.38% Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Discount upon issuance of Convertible Notes	$ 1,500,000				$ 979,000
Debt issuance costs	$ 5,200,000				$ 8,400,000
Convertible Notes, assumed effective interest rate	5.49%				4.57%
Convertible Senior Notes, Interest rate including amortization of discount upon issuance					4.91%
Convertible Notes, assumed effective interest rate	5.25%
2013 Convertible Notes [Member]
Debt Instrument [Line Items]
Convertible notes value		$ 172,000

Convertible Notes, Net - Summ_3

Convertible Notes, Net - Summary of Details of Net Book Value of Convertible Note (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Deferred financing costs	$ (20,497)	$ (16,681)
Net book value	780,951	563,911
Convertible Senior Note [Member]
Debt Instrument [Line Items]
Face Value	794,828	575,000
Unamortized discount	(12,956)	(10,279)
Deferred financing costs	(921)	(810)
Net book value	$ 780,951	$ 563,911

Convertible Notes, Net - Summ_4

Convertible Notes, Net - Summary of Details about Interest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Discount and issuance cost amortization			$ 20,993	$ 16,356
Convertible Senior Note [Member]
Debt Instrument [Line Items]
Cash coupon	$ 9,277	$ 6,247	25,333	12,732
Discount and issuance cost amortization	1,535	1,202	4,242	2,869
Total interest expense	$ 10,812	$ 7,449	$ 29,575	$ 15,601

Derivative Financial Instrume_3

Derivative Financial Instruments - Summary of Outstanding Foreign Exchange Derivatives Designated as Net Investment Hedges of Foreign Currency Risk (Detail) - Sell [Member] - Designated as Hedging Instrument [Member] - Foreign Exchange Forward [Member] - Net Investment Hedges [Member] € in Thousands, £ in Thousands, $ in Thousands, $ in Thousands	Sep. 30, 2018EUR (€)DerivativeInstrument	Sep. 30, 2018GBP (£)DerivativeInstrument	Sep. 30, 2018CAD ($)DerivativeInstrument	Sep. 30, 2018AUD ($)DerivativeInstrument	Dec. 31, 2017GBP (£)DerivativeInstrument	Dec. 31, 2017CAD ($)DerivativeInstrument
EUR [Member]
Derivative [Line Items]
Number of Instruments	1	1	1	1
Notional Amount | €	€ 185,000
GBP [Member]
Derivative [Line Items]
Number of Instruments	1	1	1	1	1	1
Notional Amount | £		£ 79,100			£ 112,700
CAD [Member]
Derivative [Line Items]
Number of Instruments	1	1	1	1	1	1
Notional Amount | $			$ 71,600			$ 95,100
AUD [Member]
Derivative [Line Items]
Number of Instruments	3	3	3	3
Notional Amount | $				$ 305,000

Derivative Financial Instrume_4

Derivative Financial Instruments - Summary of Outstanding Interest Rate Derivatives Designated as Cash Flow Hedges of Interest Rate Risk (Detail) - Cash Flow Hedges [Member] - Designated as Hedging Instrument [Member] £ in Thousands, $ in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)DerivativeInstrument	Dec. 31, 2017USD ($)DerivativeInstrument	Sep. 30, 2018CAD ($)DerivativeInstrument	Dec. 31, 2017GBP (£)DerivativeInstrument	Dec. 31, 2017CAD ($)DerivativeInstrument
Interest Rate Caps [Member] | GBP [Member] | GBP LIBOR [Member]
Derivative [Line Items]
Number of Instruments | DerivativeInstrument		3		3	3
Notional Amount | £				£ 23,370
Strike		2.00%		2.00%	2.00%
Wtd. Avg. Maturity (Years)		3 months 19 days
Interest Rate Caps [Member] | USD [Member] | USD LIBOR [Member]
Derivative [Line Items]
Number of Instruments	9	9	9	9	9
Notional Amount | $	$ 204,248	$ 204,248
Strike	2.40%	2.40%	2.40%	2.40%	2.40%
Wtd. Avg. Maturity (Years)	8 months 12 days	1 year 6 months
Interest Rate Caps [Member] | CAD [Member] | CDOR [Member]
Derivative [Line Items]
Number of Instruments | DerivativeInstrument	3	3	3	3	3
Notional Amount | $			$ 22,765		$ 23,370
Strike	2.00%	2.00%	2.00%	2.00%	2.00%
Wtd. Avg. Maturity (Years)	4 months 24 days	3 months 19 days
Interest Rate Swaps [Member] | CAD [Member] | CDOR [Member]
Derivative [Line Items]
Number of Instruments | DerivativeInstrument	4	4	4	4	4
Notional Amount | $			$ 107,822		$ 108,094
Strike	1.00%	1.00%	1.00%	1.00%	1.00%
Wtd. Avg. Maturity (Years)	8 months 12 days	1 year 4 months 24 days

Derivative Financial Instrume_5

Derivative Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of collateral posted for the net assets/liability positions	$ 7,360,000		$ 7,360,000		$ 4,120,000
Not Designated as Hedging Instrument [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivatives recorded gains (losses) during the period	$ 51,000	$ 42,000	94,000	$ 355,000
Interest Rate Swaps/Derivatives [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Reclassification from accumulated other comprehensive income (loss) as increase to interest income			$ 570,000
Reclassification from accumulated other comprehensive income, time period			12 months

Derivative Financial Instrume_6

Derivative Financial Instruments - Summary of Non-designated Hedges (Detail) - Not Designated as Hedging Instrument [Member] - EUR [Member] - Buy GBP / Sell EUR Forward [Member] € in Thousands	Sep. 30, 2018EUR (€)DerivativeInstrument	Dec. 31, 2017EUR (€)DerivativeInstrument
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Instruments | DerivativeInstrument	1	1
Amount | €	€ 12,857	€ 12,857

Derivative Financial Instrume_7

Derivative Financial Instruments - Summary of Fair Value of Derivative Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value of Derivatives in an Asset Position	$ 2,719	$ 1,214
Fair Value of Derivatives in a Liability Position	3,676	4,911
Designated as Hedging Instrument [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value of Derivatives in an Asset Position	2,556	1,214
Fair Value of Derivatives in a Liability Position	3,676	4,872
Designated as Hedging Instrument [Member] | Foreign Currency Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value of Derivatives in an Asset Position	1,514
Fair Value of Derivatives in a Liability Position	3,676	4,872
Designated as Hedging Instrument [Member] | Interest Rate Swaps/Derivatives [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value of Derivatives in an Asset Position	1,042	1,214
Not Designated as Hedging Instrument [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value of Derivatives in an Asset Position	163
Fair Value of Derivatives in a Liability Position		39
Not Designated as Hedging Instrument [Member] | Foreign Currency Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value of Derivatives in an Asset Position	$ 163
Fair Value of Derivatives in a Liability Position		$ 39

Derivative Financial Instrume_8

Derivative Financial Instruments - Summary of Effect of Derivative Financial Instruments on Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivatives	$ 1,855	$ 24,011
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income	152	388
Net Investment [Member] | Foreign Currency Contracts [Member] | Interest Expense [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivatives	1,763	23,782
Cash Flow Hedges [Member] | Interest Rate Swaps/Derivatives [Member] | Interest Expense [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income	152,000	388,000
Cash Flow Hedges [Member] | Interest Rate Swaps/Derivatives [Member] | Interest Income (Expense) [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) Recognized in OCI on Derivatives	92	228
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income	$ 152	$ 388

Derivative Financial Instrume_9

Derivative Financial Instruments - Summary of Effect of Derivative Financial Instruments on Consolidated Statements of Operations (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total interest and related expenses	$ 97,955	$ 67,891	$ 255,677	$ 168,917
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income	152		388
Interest Rate Swaps/Derivatives [Member] | Cash Flow Hedges [Member] | Interest Expense [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Gain (Loss) Reclassified from Accumulated OCI into Income	152,000		388,000
Foreign Currency Contracts [Member] | Net Investment Hedges [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net cash settlements on our foreign currency forward contracts	$ 7,600		$ 21,000

Equity - Additional Information

Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Oct. 15, 2018	Sep. 14, 2018	May 09, 2014	Aug. 31, 2018	May 31, 2013	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Mar. 25, 2014
Class of Stock [Line Items]
Total stock, shares authorized						300,000,000		300,000,000
Common stock, shares authorized						200,000,000		200,000,000		200,000,000
Preferred stock, shares authorized						100,000,000		100,000,000
Preferred stock issued						0		0
Preferred stock outstanding						0		0
Plan adoption date								Mar. 25, 2014
Number of shares sold during period					25,875,000			11,484,414	971
Net proceeds from issuance of class A common stock								$ 369,787	$ 31
Dividends paid	$ 74,200
Dividends declared per share of common stock		$ 0.62				$ 0.62	$ 0.62	$ 1.86	$ 1.86
Dividends paid per common stock	$ 0.62
Date of dividend paid								Oct. 15, 2018
Date of dividend declared								Sep. 14, 2018
Record date of dividend paid								Sep. 28, 2018
Accumulated other comprehensive loss						$ (32,849)		$ (32,849)		$ (29,706)
Net realized and unrealized gains related to changes in fair value of derivative instruments						54,300		54,300		30,600
Cumulative unrealized currency translation adjustment on assets and liabilities denominated in foreign currencies						87,100		87,100		60,300
Multifamily [Member] | Joint Venture [Member]
Class of Stock [Line Items]
Total equity						48,100		48,100		42,300
Equity interests owned by Blackstone Mortgage Trust, Inc.						40,900		40,900		36,000
Non-controlling interests						$ 7,200		$ 7,200		$ 6,300
Dividend Reinvestment and Direct Stock Purchase Plan [Member]
Class of Stock [Line Items]
Reserved for issuance of class A common stock						9,995,647		9,995,647			10,000,000
Class A Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued under dividend reinvestment program						403	428	1,279	971
Number of shares sold during period				6,900,000				11,483,135
Net proceeds from issuance of class A common stock				$ 222,275				$ 369,787
ATM Agreements [Member] | Class A Common Stock [Member]
Class of Stock [Line Items]
Aggregate sales price			$ 200,000
Number of shares sold during period								4,583,135	0
Net proceeds from issuance of class A common stock								$ 147,512
Aggregate sales price remaining available						$ 38,600		$ 38,600

Equity - Summary of Class A Com

Equity - Summary of Class A Common Stock Issuances (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		9 Months Ended
	Aug. 31, 2018	May 31, 2013	Sep. 30, 2018	Sep. 30, 2017
Class of Stock [Line Items]
Shares issued		25,875,000	11,484,414	971
Share issue price			$ 32.73
Net proceeds			$ 369,787	$ 31
Class A Common Stock [Member]
Class of Stock [Line Items]
Shares issued	6,900,000		11,483,135
Share issue price	$ 32.60		$ 32.65
Net proceeds	$ 222,275		$ 369,787
Class A Common Stock [Member] | ATM Agreements [Member]
Class of Stock [Line Items]
Shares issued			4,583,135	0
Share issue price			$ 32.73
Net proceeds			$ 147,512

Equity - Summary of Class A C_2

Equity - Summary of Class A Common Stock Issuances (Parenthetical) (Detail) - $ / shares	8 Months Ended	9 Months Ended
	Aug. 31, 2018	Sep. 30, 2018
Equity [Abstract]
Share issue price		$ 32.73
Net proceeds after sales discounts and commissions	$ 32.24	$ 32.26

Equity - Schedule of Movement i

Equity - Schedule of Movement in Outstanding Shares of Class A Common Stock, Restricted Class A Common Stock and Deferred Stock Units (Detail) - shares	1 Months Ended	9 Months Ended
	May 31, 2013	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Beginning balance		108,081,077	94,709,290
Issuance of class A common stock	25,875,000	11,484,414	971
Issuance of restricted class A common stock, net		300,921	286,773
Issuance of deferred stock units		23,730	20,560
Ending balance		119,890,142	95,017,594

Equity - Schedule of Movement_2

Equity - Schedule of Movement in Outstanding Shares of Class A Common Stock, Restricted Class A Common Stock and Deferred Stock Units (Parenthetical) (Detail) - Class A Common Stock [Member] - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Class of Stock [Line Items]
Deferred stock units held by directors	220,947	189,587	220,947	189,587
Common stock, shares issued under dividend reinvestment program	403	428	1,279	971

Equity - Schedule of Dividend A

Equity - Schedule of Dividend Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 14, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Dividends declared per share of common stock	$ 0.62	$ 0.62	$ 0.62	$ 1.86	$ 1.86
Total dividends declared		$ 74,195	$ 58,793	$ 210,369	$ 176,374

Equity - Schedule of Basic and

Equity - Schedule of Basic and Diluted Earnings Per Share, or EPS, Based on Weighted-Average of Both Restricted and Unrestricted Class A Common Stock Outstanding (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income	$ 78,165	$ 57,722	$ 211,436	$ 159,741
Weighted-average shares outstanding, basic and diluted	116,203,140	95,013,087	111,251,864	95,004,188
Per share amount, basic and diluted	$ 0.67	$ 0.61	$ 1.90	$ 1.68

Other Expenses - Additional Inf

Other Expenses - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Management fee - percent of outstanding equity balance			1.50%
Incentive fee computation-percent of the product per agreement			20.00%
Incentive fee computation-percent of outstanding Equity per annum			7.00%
Management fees description			Manager is entitled to an incentive fee in an amount equal to the product of (i) 20% and (ii) the excess of (a) our Core Earnings (as defined in our Management Agreement) for the previous 12-month period over (b) an amount equal to 7.00% per annum multiplied by our outstanding Equity, provided that our Core Earnings over the prior three-year period is greater than zero. Core Earnings, as defined in our Management Agreement, is generally equal to our net income (loss) prepared in accordance with GAAP, excluding (i) certain non-cash items (ii) the net income (loss) related to our legacy portfolio and (iii) incentive management fees.
Management fees	$ 18,368	$ 13,243	$ 56,248	$ 40,557
Accrued management and incentive fees payable	18,368		18,368		$ 14,284
Manager [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Management fees	12,100	9,500	34,200	28,600
Total incentive compensation payments	6,300	$ 3,700	22,000	$ 11,900
Accrued management and incentive fees payable	$ 18,400		$ 18,400		$ 14,300

Other Expenses - Schedule of Ge

Other Expenses - Schedule of General and Administrative Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Professional services	$ 1,022	$ 933	$ 3,383	$ 2,811
Operating and other costs	687	489	2,026	1,424
Subtotal	1,709	1,422	5,409	4,235
Non-cash compensation expenses
Restricted class A common stock earned	6,609	5,819	20,113	17,496
Director stock-based compensation	125	125	375	313
Subtotal	6,734	5,944	20,488	17,809
Total BXMT expenses	8,443	7,366	25,897	22,044
Other expenses		53		175
Total general and administrative expenses	$ 8,443	$ 7,419	$ 25,897	$ 22,219

Other Expenses - Schedule of _2

Other Expenses - Schedule of General and Administrative Expenses (Parenthetical) (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Multifamily [Member] | Joint Venture [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Expenses related Multifamily Joint Venture.	$ 77,000	$ 112,000	$ 302,000	$ 112,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2013	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Tax Credit Carryforward [Line Items]
Annual distribution of net taxable income for U.S. federal income tax not to apply to our earnings that we distribute (percent)				90.00%
Net taxable income subject to distribution (percent)				100.00%
Excise tax rate				4.00%
Income tax provision		$ 48,000	$ 83,000	$ 272,000	$ 265,000
Deferred tax assets		0		0		$ 0
Deferred tax liabilities		0		$ 0		$ 0
U.S. federal corporate income tax rate				21.00%		35.00%
Common stock, shares issued	25,875,000			11,484,414	971
Net operating losses carried forward						$ 159,000,000
NOLs expiration date						Dec. 31, 2029
Open tax year				2015 2016 2017
Internal Revenue Service [Member]
Tax Credit Carryforward [Line Items]
Net operating losses limit per annum		$ 2,000,000		$ 2,000,000
Net operating losses limitations				The availability of our NOLs is generally limited to $2.0 million per annum

Stock-Based Incentive Plans - A

Stock-Based Incentive Plans - Additional Information (Detail) $ / shares in Units, $ in Millions	Sep. 30, 2018USD ($)Plansshares	Sep. 30, 2018USD ($)Plansshares	Jun. 29, 2018$ / shares	Dec. 31, 2017shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of benefit plans | Plans	9	9
Restricted Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares, vesting period		3 years
Number of shares of restricted class A common stock outstanding	1,380,855	1,380,855		1,484,175
Unrecognized compensation cost relating to nonvested share-based compensation | $	$ 33.9	$ 33.9
Unrecognized compensation cost expected to be recognized over weighted average period	1 year
Nonvested share-based compensation, closing price | $ / shares			$ 31.43
Stock Incentive Current Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available under plan	0	0
Maximum number of shares available under plan	5,000,000	5,000,000
Expired Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available under plan	0	0
Vest in 2018 [Member] | Restricted Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of restricted class A common stock outstanding	448,474	448,474
Vest in 2019 [Member] | Restricted Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of restricted class A common stock outstanding	616,168	616,168
Vest in 2020 [Member] | Restricted Class A Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of restricted class A common stock outstanding	316,213	316,213

Stock-Based Incentive Plans - M

Stock-Based Incentive Plans - Movement in Outstanding Shares of Restricted Class A Common Stock and Weighted-Average Grant Date Fair Value Per Share (Detail) - Restricted Class A Common Stock [Member]	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Class A Common Stock, Beginning Balance | shares	1,484,175
Restricted Class A Common Stock, Granted | shares	318,741
Restricted Class A Common Stock, Vested | shares	(404,241)
Restricted Class A Common Stock, Forfeited | shares	(17,820)
Restricted Class A Common Stock, Ending Balance | shares	1,380,855
Weighted-Average Grant Date Fair Value Per Share, Beginning Balance | $ / shares	$ 30.61
Weighted-Average Grant Date Fair Value Per Share, Granted | $ / shares	31.83
Weighted-Average Grant Date Fair Value Per Share, Vested | $ / shares	28.89
Weighted-Average Grant Date Fair Value Per Share, Forfeited | $ / shares	30.44
Weighted-Average Grant Date Fair Value Per Share, Ending Balance | $ / shares	$ 31.40

Fair Values - Assets and Liabil

Fair Values - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets
Derivatives	$ 2,719	$ 1,214
Liabilities
Derivatives	3,676	4,911
Recurring [Member]
Assets
Derivatives	2,719	1,214
Liabilities
Derivatives	3,676	4,911
Level 2 [Member] | Recurring [Member]
Assets
Derivatives	2,719	1,214
Liabilities
Derivatives	$ 3,676	$ 4,911

Fair Values - Schedule of Detai

Fair Values - Schedule of Details of Book Value, Face Amount, and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Financial assets
Cash and cash equivalents, face amount	$ 86,987	$ 69,654	$ 61,221
Restricted cash		32,864
Loans receivable, net, face amount	12,260,103	10,108,226
Debt securities held-to-maturity	96,050
Debt securities held-to-maturity	99,000
Financial liabilities
Secured debt agreements, net, face amount	6,862,256	5,290,536
Loan participations sold, net	81,044	80,415
Loan participations sold, net, face amount	106,259	141,119
Securitized debt obligations, net	1,284,362	1,282,412
Securitized debt obligations, net,face amount	1,292,120	1,292,120
Book Value [Member]
Financial assets
Cash and cash equivalents	86,987	69,654
Restricted cash		32,864
Loans receivable, net	12,176,516	10,056,732
Debt securities held-to-maturity	96,050
Financial liabilities
Secured debt agreements, net	6,841,759	5,273,855
Loan participations sold, net	81,044	80,415
Securitized debt obligations, net	1,284,362	1,282,412
Convertible notes, net	780,951	563,911
Fair Value [Member]
Financial assets
Cash and cash equivalents	86,987	69,654
Restricted cash		32,864
Loans receivable, net	12,261,013	10,112,331
Debt securities held-to-maturity	97,607
Financial liabilities
Secured debt agreements, net	6,862,256	5,290,536
Loan participations sold, net	81,170	80,706
Securitized debt obligations, net	1,297,032	1,292,589
Convertible notes, net	832,407	610,201
Convertible Senior Note [Member]
Financial liabilities
Convertible notes, net, face amount	794,828	575,000
Senior Participation [Member]
Financial liabilities
Loan participations sold, net	81,044	80,415
Loan participations sold, net, face amount	$ 81,170	$ 80,706

Variable Interest Entities - Su

Variable Interest Entities - Summary of Assets and Liabilities of Consolidated CLO and 2017 Single Asset Securitization VIE (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets:
Assets	$ 1,500,000	$ 1,500,000
VIE [Member]
Assets:
Assets	1,504,899	1,502,407
Liabilities:
Liabilities	1,286,231	1,283,791
VIE [Member] | Loans Receivable [Member]
Assets:
Assets	1,500,000	1,500,000
VIE [Member] | Other Assets [Member]
Assets:
Assets	4,899	2,407
VIE [Member] | Securitized Debt Obligations, Net [Member]
Liabilities:
Liabilities	1,284,362	1,282,412
VIE [Member] | Other Liabilities [Member]
Liabilities:
Liabilities	$ 1,869	$ 1,379

Variable Interest Entities - Ad

Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2018	Jul. 31, 2018	Dec. 31, 2017	Jun. 30, 2017
Variable Interest Entity [Line Items]
Loan contributed to securitization	$ 517,500
Subordinate risk retention interest notional amount	99,000
Single asset securitization principal amount		$ 1,000,000		$ 474,600
2018 Single Asset Securitization [Member]
Variable Interest Entity [Line Items]
Single asset securitization principal amount	1,000,000
Maximum exposure to loss	96,100
Collateral Assets [Member]
Variable Interest Entity [Line Items]
Single asset securitization principal amount	1,678,963		$ 1,656,406
Collateral Assets [Member] | Collateralized Loan Obligations [Member]
Variable Interest Entity [Line Items]
Single asset securitization principal amount	$ 1,000,000		$ 1,000,000

Transactions with Related Par_2

Transactions with Related Parties - Additional Information (Detail) € in Billions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)shares	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)SecurityLoanshares	Sep. 30, 2017USD ($)SecurityLoan	Dec. 31, 2017USD ($)SecurityLoanshares	Jul. 31, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Mar. 31, 2018EUR (€)	Jun. 30, 2017USD ($)
Related Party Transaction [Line Items]
Accrued management and incentive fees payable	$ 18,368,000		$ 18,368,000		$ 14,284,000
Common stock value	1,197,000		1,197,000		1,079,000
Non-cash expenses			20,488,000	$ 17,809,000
Loan face amount	$ 12,260,103,000		$ 12,260,103,000		$ 10,108,226,000
Number of Loans | SecurityLoan			112		110
Fully subscribed offering costs						$ 1,000,000,000				$ 474,600,000
Senior Term Facility [Member]
Related Party Transaction [Line Items]
Loan face amount | €									€ 7.3
Senior term facility | €									€ 1
Minority participation in senior term facility								14.00%	14.00%
Third-Party Service Provider [Member]
Related Party Transaction [Line Items]
Administrative services expenses incurred		$ 87,000		254,000
Restricted Class A Common Stock [Member]
Related Party Transaction [Line Items]
Shares held | shares	1,380,855		1,380,855		1,484,175
Restricted shares, vesting period	3 years
Manager [Member]
Related Party Transaction [Line Items]
Management Agreement expiration date			Dec. 19, 2017
Management Agreement renewal term, description			The current term of which expires on December 19, 2018, and will be automatically renewed for a one-year term upon such date and each anniversary thereafter unless earlier terminated.
Management Agreement renewal term, period			1 year
Accrued management and incentive fees payable	$ 18,400,000		$ 18,400,000		$ 14,300,000
Management fees paid to Manager	22,400,000	14,400,000	52,200,000	40,100,000
Expenses reimbursed to Manager	$ 167,000	59,000	$ 572,000	$ 325,000
Number of Loans | SecurityLoan			3	5
Expenses incurred on insurance agency transaction of affiliate with loan borrower			$ 0	$ 0
Income received on insurance agency transaction of affiliate with loan borrower			$ 0	0
Securitized debt obligations issued, aggregate amount						$ 116,100,000				$ 72,900,000
Manager [Member] | Senior Loan [Member]
Related Party Transaction [Line Items]
Loan face amount							$ 1,000,000,000	$ 330,000,000
Manager [Member] | Senior Loan [Member] | Partially Owned Properties [Member]
Related Party Transaction [Line Items]
Ownership interest in joint venture							50.00%
Manager [Member] | Class A Common Stock [Member] | Restricted Class A Common Stock [Member]
Related Party Transaction [Line Items]
Shares held | shares	675,333		675,333
Common stock value	$ 21,200,000		$ 21,200,000
Non-cash expenses	$ 3,200,000	$ 2,900,000	9,600,000	8,700,000
Manager [Member] | Class A Common Stock [Member] | Restricted Class A Common Stock [Member] | Stock Incentive Current Plan [Member]
Related Party Transaction [Line Items]
Restricted shares, vesting period	3 years
Affiliates of Manager [Member]
Related Party Transaction [Line Items]
Special servicing fees			0	$ 0
Affiliates of Manager [Member] | Third-Party Service Provider [Member]
Related Party Transaction [Line Items]
Administrative services expenses incurred	$ 90,000		$ 384,000
Blackstone-Advised Investment Vehicles, or the Funds [Member] | Senior Term Facility [Member]
Related Party Transaction [Line Items]
Ownership interest in joint venture								51.00%	51.00%

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018USD ($)LoansDirectors	Dec. 31, 2017USD ($)
Commitments And Contingencies [Line Items]
Number of loans receivable | Loans	80
Number of independent directors entitled to annual compensation | Directors	5
Loans Receivable [Member]
Commitments And Contingencies [Line Items]
Unfunded loan commitments	$ 3,046,350,000	$ 1,573,107,000
Five Independent Board of Directors [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	175,000
Annual cash compensation paid in cash	75,000
Annual cash compensation paid in the form of deferred stock units	100,000
Chairperson of Audit Committee [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	20,000
Audit Committee Members [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	10,000
Compensation and Corporate Governance Committees [Member]
Commitments And Contingencies [Line Items]
Annual cash compensation	$ 10,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Principal Contractual Obligations (Detail) $ in Thousands	Sep. 30, 2018USD ($)
Debt Instrument [Line Items]
Total Obligation	$ 7,657,084
Less Than 1 Year	445,582
1 to 3 Years	2,393,008
3 to 5 Years	4,735,294
More Than 5 Years	83,200
Secured Debt [Member]
Debt Instrument [Line Items]
Total Obligation	6,862,256
Less Than 1 Year	273,254
1 to 3 Years	2,393,008
3 to 5 Years	4,112,794
More Than 5 Years	83,200
Convertible Debt [Member]
Debt Instrument [Line Items]
Total Obligation	794,828
Less Than 1 Year	172,328
3 to 5 Years	$ 622,500

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Principal Contractual Obligations (Parenthetical) (Detail) $ in Millions	Sep. 30, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Loan participations sold excluded from contractual obligations	$ 81.2
Non-consolidated senior interests excluded from contractual obligations	466.7
Securitized debt obligations excluded from contractual obligations	$ 1,300