| Document and Entity Information Document | May 11, 2020 | Feb. 19, 2020 |
| Document And Entity Information [Abstract] | ||
| Document Type | 8-K | |
| Document Period End Date | May 11, 2020 | |
| Entity Registrant Name | National Health Investors Inc | |
| Entity Incorporation, State or Country Code | MD | |
| Entity File Number | 001-10822 | |
| 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 | |
| Written Communications | false | |
| Soliciting Material | false | |
| Pre-commencement Tender Offer | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Title of 12(b) Security | Common Stock, $0.01 par value | |
| Trading Symbol | NHI | |
| Security Exchange Name | NYSE | |
| Entity Emerging Growth Company | false | |
| Entity Central Index Key | 0000877860 | |
| Amendment Flag | false |
