| Document and Entity Information | Feb. 19, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 19, 2021 |
| Entity File Number | 001-39134 |
| Entity Registrant Name | BROADMARK REALTY CAPITAL INC. |
| Entity Incorporation, State or Country Code | MD |
| Entity Tax Identification Number | 84-2620891 |
| Entity Address, Address Line One | 1420 Fifth Avenue, Suite 2000 |
| Entity Address, City or Town | Seattle |
| Entity Address, State or Province | WA |
| Entity Address, Postal Zip Code | 98101 |
| City Area Code | 206 |
| Local Phone Number | 971-0800 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001784797 |
| Amendment Flag | false |
| Common Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common stock, par value $0.001 per share |
| Trading Symbol | BRMK |
| Security Exchange Name | NYSE |
| Warrant [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Warrants, each exercisable for one fourth (1/4th) share of Common Stock at an exercise price of $2.875 per one fourth (1/4th) share |
| Trading Symbol | BRMK WS |
| Security Exchange Name | NYSEAMER |
