Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity Noncontrolling Interest (Details)

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Stockholders' Equity Noncontrolling Interest (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Nov. 01, 2017
Dec. 31, 2017
Jun. 28, 2017
Equity [Abstract]      
Shares of Granite Point Mortgage Trust Inc. common stock received in exchange for contribution (in shares)     33,100,000
Ownership percentage in Granite Point Mortgage Trust Inc.     76.50%
Shares issued by Granite Point Mortgage Trust Inc. in initial public offering (in shares)   10,000,000  
Price per share issued by Granite Point Mortgage Trust Inc. in initial public offering (in usd per share)     $ 19.50
Net proceeds received by Granite Point Mortgage Trust Inc. in initial public offering   $ 195,000  
Gross proceeds received by Granite Point Mortgage Trust Inc. in initial public offering   181,900  
Issuance costs incurred by Granite Point Mortgage Trust Inc. in initial public offering   $ 13,100  
Number of shares of common stock of Granite Point Mortgage Trust Inc distributed via special dividend (in shares) 33,100,000