Document And Entity Information - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Feb. 15, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-10822
Entity Registrant Name	National Health Investors Inc
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	62-1470956
Entity Address, Address Line One	222 Robert Rose Drive
Entity Address, City or Town	Murfreesboro
Entity Address, State or Province	TN
Entity Address, Postal Zip Code	37129
City Area Code	(615)
Local Phone Number	890-9100
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	NHI
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 2,580,970
Entity Common Stock, Shares Outstanding		45,185,992
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement for its 2021 annual meeting of stockholders are incorporated by reference into Part III, Items 10, 11, 12, 13, and 14 of this Form 10-K.
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0000877860
Current Fiscal Year End Date	--12-31
ICFR Auditor Attestation Flag	true