Note 8 - 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
	Mar. 31, 2020	Mar. 31, 2019
Basic:
Weighted average common shares outstanding (in shares)	15,294,777	15,256,189
Net income/(loss) attributable to National HealthCare Corporation	$ (26,852)	$ 21,269
Earnings/(loss) per common share, basic (in dollars per share)	$ (1.76)	$ 1.39
Diluted:
Weighted average common shares outstanding (in shares)	15,294,777	15,256,189
Effects of dilutive instruments (in shares)	0	67,936
Weighted average common shares outstanding (in shares)	15,294,777	15,324,125
Net income/(loss) attributable to National HealthCare Corporation	$ (26,852)	$ 21,269
Earnings/(loss) per common share, diluted (in dollars per share)	$ (1.76)	$ 1.39