Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity Schedule of Common Dividends Declared (Details)

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Stockholders' Equity Schedule of Common Dividends Declared (Details) - $ / shares
3 Months Ended
Nov. 01, 2017
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Class of Stock [Line Items]            
Dividends declared per common share (in usd per share)   $ 0.47       $ 0.50
Number of shares of common stock of Granite Point Mortgage Trust Inc distributed via special dividend (in shares) 33,100,000          
Common Stock [Member]            
Class of Stock [Line Items]            
Declaration Date   Mar. 20, 2018 Dec. 14, 2017 Sep. 14, 2017 Jun. 15, 2017 Mar. 14, 2017
Record Date   Apr. 02, 2018 Dec. 26, 2017 Sep. 29, 2017 Jun. 30, 2017 Mar. 31, 2017
Payment Date   Apr. 27, 2018 Dec. 29, 2017 Oct. 27, 2017 Jul. 27, 2017 Apr. 27, 2017
Dividends declared per common share (in usd per share)   $ 0.47 $ 0.47 $ 0.52 $ 0.52 $ 0.5