Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2019	Mar. 31, 2020	Jun. 30, 2019
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	333-232308
Entity Registrant Name	Hartman vREIT XXI, Inc.
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	38-3978914
Entity Address, Address Line One	2909 Hillcroft
Entity Address, Address Line Two	Suite 420
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77057
City Area Code	713
Local Phone Number	467-2222
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Public Float			$ 0
Entity Common Stock, Shares Outstanding		8,619,181
Amendment Flag	false
Entity Central Index Key	0001654948
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY