Quarterly report pursuant to Section 13 or 15(d)

Equity Incentive Plan Granite Point Mortgage Trust Inc. Equity Incentive Plan (Details)

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Equity Incentive Plan Granite Point Mortgage Trust Inc. Equity Incentive Plan (Details) - Granite Point Mortgage Trust Inc. 2017 Equity Incentive Plan [Member] - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Compensation costs related to restricted common stock $ 687 $ 687
Director [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of restricted common shares granted during period under equity incentive plan (in shares) 14,103  
Key Employees [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of restricted common shares granted during period under equity incentive plan (in shares) 150,000