Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 01, 2022	Jun. 30, 2021
Document Information [Line Items]
Entity Central Index Key	0001065201
Entity Registrant Name	AMERINST INSURANCE GROUP LTD
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2021
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Document Transition Report	false
Entity File Number	000-28249
Entity Incorporation, State or Country Code	D0
Entity Tax Identification Number	98-0207447
Entity Address, Address Line One	25 Church Street, Continental Building
Entity Address, City or Town	Hamilton
Entity Address, Country	BM
Entity Address, Postal Zip Code	HM GX
City Area Code	441
Local Phone Number	295-2185
Title of 12(b) Security	COMMON SHARES, PAR VALUE $1.00 PER SHARE
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	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		995,253
Entity Public Float			$ 5,893,827
Auditor Name	Deloitte Ltd.
Auditor Location	Hamilton Bermuda
Auditor Firm ID	5230