Note 7 - Earning 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								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic:
Weighted average common shares outstanding (in shares)									15,270,154	15,224,886	15,189,920
Net income attributable to common stockholders of National Healthcare Corporation									$ 68,211	$ 58,964	$ 56,205
Basic earnings per share (in dollars per share)	$ 0.91	$ 1.27	$ 90	$ 1.39	$ 1.19	$ 1.39	$ 1.47	$ (0.18)	$ 4.47	$ 3.87	$ 3.70
Diluted:
Weighted average common shares outstanding (in shares)									15,270,154	15,224,886	15,189,920
Assumed average common shares outstanding (in shares)									15,360,046	15,236,826	15,218,962
Net income attributable to common stockholders of National Healthcare Corporation									$ 68,211	$ 58,964	$ 56,205
Diluted earnings per share (in dollars per share)	$ 0.89	$ 1.27	$ 89	$ 1.39	$ 1.19	$ 1.39	$ 1.47	$ (0.18)	$ 4.44	$ 3.87	$ 3.69
Share-based Payment Arrangement, Option [Member]
Diluted:
Dilutive effect of share-based awards (in shares)									89,892	11,940	29,042