Note 9 - Earnings Per Share - Summary of Earnings and Weighted Average Number of Common Shares Used in Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Basic:
Weighted average common shares outstanding (in shares)	15,445,569	15,364,043	15,438,375	15,347,042
Net income/(loss) attributable to National HealthCare Corporation	$ (2,429)	$ (3,348)	$ 16,092	$ 122,802
Earnings/(loss) per common share, basic (in dollars per share)	$ (0.16)	$ (0.22)	$ 1.04	$ 8.00
Diluted:
Weighted average common shares outstanding (in shares)	15,445,569	15,364,043	15,438,375	15,347,042
Effects of dilutive instruments (in shares)	0	0	38,728	67,641
Weighted average common shares outstanding (in shares)	15,445,569	15,364,043	15,477,103	15,414,683
Net income/(loss) attributable to National HealthCare Corporation	$ (2,429)	$ (3,348)	$ 16,092	$ 122,802
Earnings/(loss) per common share, diluted (in dollars per share)	$ (0.16)	$ (0.22)	$ 1.04	$ 7.97