XML 53 R83.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Equity - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Jan. 15, 2020
Nov. 14, 2018
May 31, 2013
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Mar. 25, 2014
Class of Stock [Line Items]              
Total stock, shares authorized       300,000,000      
Common stock, shares authorized       200,000,000 200,000,000    
Preferred stock, shares authorized       100,000,000      
Preferred stock issued       0      
Preferred stock outstanding       0      
Plan adoption date       Mar. 25, 2014      
Number of shares sold during period     25,875,000 10,535,842 14,568,431 12,421,401  
Dividends paid $ 83,700,000            
Dividends paid per common stock $ 0.62            
Date of dividend paid       Jan. 15, 2020      
Date of dividend declared       Dec. 16, 2019      
Record date of dividend paid       Dec. 31, 2019      
Accumulated other comprehensive loss       $ 16,233,000 $ 34,222,000    
Net realized and unrealized gains related to changes in fair value of derivative instruments       64,500,000 70,400,000    
Cumulative unrealized currency translation adjustment on assets and liabilities denominated in foreign currencies       80,700,000 104,600,000    
Net proceeds from issuance of class A common stock       372,337,000 476,420,000 $ 391,558,000  
Multifamily [Member] | Joint Venture [Member]              
Class of Stock [Line Items]              
Total equity       147,300,000 69,900,000    
Equity interests owned by Blackstone Mortgage Trust, Inc.       125,200,000 59,400,000    
Non-controlling interests       $ 22,100,000 $ 10,500,000    
Dividend Reinvestment and Direct Stock Purchase Plan [Member]              
Class of Stock [Line Items]              
Reserved for issuance of class A common stock       9,994,024     10,000,000
Class A Common Stock [Member]              
Class of Stock [Line Items]              
Common stock, shares issued under dividend reinvestment program       1,214 1,688 1,401  
Number of shares sold during period       10,534,628 14,566,743 12,420,000  
Net proceeds from issuance of class A common stock       $ (372,341) $ 476,420 $ 391,558  
Class A Common Stock [Member] | Dividend Reinvestment and Direct Stock Purchase Plan [Member]              
Class of Stock [Line Items]              
Common stock, shares issued under dividend reinvestment program       1,214 1,688 1,401  
Class A Common Stock [Member] | ATM Agreements [Member]              
Class of Stock [Line Items]              
Aggregate sales price   $ 500,000,000.0          
Number of shares sold during period       7,666,743      
Aggregate sales price remaining available       $ 363,800,000      
Net proceeds from issuance of class A common stock       $ 254,100,000      
Class A Common Stock [Member] | BXMT At The Market Agreement [Member]              
Class of Stock [Line Items]              
Number of shares sold during period       1,909,628      
Net proceeds from issuance of class A common stock       $ 65,400,000