| Cover | Jun. 14, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jun. 14, 2021 |
| Current Fiscal Year End Date | --12-31 |
| Entity File Number | 001-35845 |
| Entity Registrant Name | LUMENT FINANCE TRUST, INC. |
| Entity Central Index Key | 0001547546 |
| Entity Tax Identification Number | 45-4966519 |
| Entity Incorporation, State or Country Code | MD |
| Entity Address, Address Line One | 230 Park Avenue |
| Entity Address, Address Line Two | 23rd Floor |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10169 |
| City Area Code | 212 |
| Local Phone Number | 521-6323 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $0.01 par value per share |
| Trading Symbol | LFT |
| Security Exchange Name | NYSE |
| Redeemable Preferred Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 7.875% Series A Cumulative Redeemable Preferred Stock, $0.01 par value per share |
| Trading Symbol | LFTPrA |
| Security Exchange Name | NYSE |
