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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Weighted average common shares outstanding (in shares)									15,224,886	15,189,920	15,134,518
Net income attributable to common stockholders of National Healthcare Corporation	$ 18,152	$ 21,142	$ 22,461	$ (2,791)	$ 21,470	$ 11,352	$ 10,655	$ 12,728	$ 58,964	$ 56,205	$ 50,538
Basic earnings per share (in dollars per share)	$ 1.19	$ 1.39	$ 1.48	$ (0.18)	$ 1.41	$ 0.75	$ 0.70	$ 0.84	$ 3.87	$ 3.70	$ 3.34
Diluted (in shares)									15,236,826	15,218,962	15,206,997
Diluted earnings per share (in dollars per share)	$ 1.19	$ 1.39	$ 1.47	$ (0.18)	$ 1.41	$ 0.75	$ 0.70	$ 0.84	$ 3.87	$ 3.69	$ 3.32
Employee Stock Option [Member]
Dilutive effect of share-based awards (in shares)									11,940	29,042	24,176
Restricted Stock [Member]
Dilutive effect of share-based awards (in shares)											48,303