| Document and Entity Information | Nov. 11, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 11, 2021 |
| Entity Registrant Name | KLDiscovery Inc. |
| Entity Central Index Key | 0001752474 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Entity File Number | 001-38789 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 61-1898603 |
| Entity Address, Address Line One | 8201 Greensboro Dr. |
| Entity Address, Address Line Two | Suite 300 |
| Entity Address, City or Town | McLean |
| Entity Address, State or Province | VA |
| Entity Address, Postal Zip Code | 22102 |
| City Area Code | 703 |
| Local Phone Number | 288-3380 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
