| Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] |
| | | Three Months Ended September 30 | | | Nine Months Ended September 30 | |
| | | 2026 | | | 2025 | | | 2026 | | | 2025 | |
| Basic: | | | | | | | | | | | | | | | | |
| Weighted average common shares outstanding | | | 15,638,814 | | | | 15,484,464 | | | | 15,599,724 | | | | 15,461,804 | |
| Net income attributable to National HealthCare Corporation | | $ | 13,637 | | | $ | 39,239 | | | $ | 89,813 | | | $ | 95,166 | |
| Earnings per common share, basic | | $ | 0.87 | | | $ | 2.53 | | | $ | 5.76 | | | $ | 6.15 | |
| | | | | | | | | | | | | | | | | |
| Diluted: | | | | | | | | | | | | | | | | |
| Weighted average common shares outstanding | | | 15,638,814 | | | | 15,484,464 | | | | 15,599,724 | | | | 15,461,804 | |
| Effects of dilutive instruments | | | 326,081 | | | | 180,066 | | | | 267,233 | | | | 151,701 | |
| Weighted average common shares outstanding | | | 15,964,895 | | | | 15,664,530 | | | | 15,866,957 | | | | 15,613,505 | |
| | | | | | | | | | | | | | | | | |
| Net income attributable to National HealthCare Corporation | | $ | 13,637 | | | $ | 39,239 | | | $ | 89,813 | | | $ | 95,166 | |
| Earnings per common share, diluted | | $ | 0.85 | | | $ | 2.50 | | | $ | 5.66 | | | $ | 6.10 | |
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