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		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Basic:
Weighted average common shares outstanding (in shares)	15,452,402	15,349,162	15,434,718	15,338,400
Net income attributable to National HealthCare Corporation	$ 3,203	$ 104,883	$ 18,521	$ 126,150
Earnings per common share, basic (in dollars per share)	$ 0.21	$ 6.83	$ 1.20	$ 8.22
Diluted:
Weighted average common shares outstanding (in shares)	15,452,402	15,349,162	15,434,718	15,338,400
Effects of dilutive instruments (in shares)	34,721	69,850	40,835	66,234
Weighted average common shares outstanding (in shares)	15,487,123	15,419,012	15,475,553	15,404,634
Net income attributable to National HealthCare Corporation	$ 3,203	$ 104,883	$ 18,521	$ 126,150
Earnings per common share, diluted (in dollars per share)	$ 0.21	$ 6.80	$ 1.20	$ 8.19