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, 2019	Mar. 31, 2018
Basic:
Weighted average common shares outstanding (in shares)	15,256,189	15,216,635
Net income (loss) attributable to National HealthCare Corporation	$ 21,269	$ (2,791)
Earnings (loss) per common share, basic (in dollars per share)	$ 1.39	$ (0.18)
Diluted:
Weighted average common shares outstanding (in shares)	15,256,189	15,216,635
Effects of dilutive instruments (in shares)	67,936
Weighted average common shares outstanding (in shares)	15,324,125	15,216,635
Net income (loss) attributable to National HealthCare Corporation	$ 21,269	$ (2,791)
Earnings (loss) per common share, diluted (in dollars per share)	$ 1.39	$ (0.18)