Quarterly report pursuant to Section 13 or 15(d)

Equity Schedule of Dividends Declared (Details)

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Equity Schedule of Dividends Declared (Details) - $ / shares
 3 Months Ended 9 Months Ended
Nov. 01, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Class of Stock [Line Items]                
Dividends declared per common share (in usd per share)   $ 0.52       $ 0.46 $ 1.54 $ 1.38
Granite Point Mortgage Trust Inc. [Member]                
Class of Stock [Line Items]                
Dividends declared per common share (in usd per share)   $ 0.32            
Series A Preferred Stock                
Class of Stock [Line Items]                
Declaration Date   Sep. 14, 2017 Jun. 15, 2017          
Record Date   Oct. 12, 2017 Jul. 12, 2017          
Payment Date   Oct. 27, 2017 Jul. 27, 2017          
Dividends declared per preferred share (in usd per share)   $ 0.50781 $ 0.75043          
Series B Preferred Stock                
Class of Stock [Line Items]                
Declaration Date   Sep. 14, 2017            
Record Date   Oct. 12, 2017            
Payment Date   Oct. 27, 2017            
Dividends declared per preferred share (in usd per share)   $ 0.51892            
Common Stock [Member]                
Class of Stock [Line Items]                
Declaration Date   Sep. 14, 2017 Jun. 15, 2017 Mar. 14, 2017 Dec. 15, 2016 Sep. 15, 2016    
Record Date   Sep. 29, 2017 Jun. 30, 2017 Mar. 31, 2017 Dec. 30, 2016 Sep. 30, 2016    
Payment Date   Oct. 27, 2017 Jul. 27, 2017 Apr. 27, 2017 Jan. 27, 2017 Oct. 20, 2016    
Dividends declared per common share (in usd per share)   $ 0.52 $ 0.52 $ 0.5 $ 0.48 $ 0.46    
Subsequent Event [Member]                
Class of Stock [Line Items]                
Number of shares of common stock of Granite Point Mortgage Trust Inc distributed via special dividend (in shares) 33,100,000