Cover Page - shares	3 Months Ended
	Mar. 31, 2021	May 13, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2021
Entity Registrant Name	KLDiscovery Inc.
Entity Central Index Key	0001752474
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Small Business	true
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		42,550,148
Entity File Number	001-38789
Entity Tax Identification Number	61-1898603
Entity Address, Address Line One	8201 Greensboro Drive
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
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false