Interim Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Noncontrolling Interest [Member]	Total
Balance (in shares) at Dec. 31, 2016	15,162,938
Balance at Dec. 31, 2016	$ 152	$ 211,457	$ 391,934	$ 66,068		$ 669,611
Net income (loss) attributable to National HealthCare Corporation			12,728			12,728
Net loss attributable to noncontrolling interest					(95)	(95)
Equity contributed by noncontrolling interest					970	970
Other comprehensive income (loss)				(567)		(567)
Stock–based compensation		92				92
Shares sold – options exercised (in shares)	16,992
Shares sold – options exercised		817				817
Dividends declared to common stockholders			(6,831)			(6,831)
Balance (in shares) at Mar. 31, 2017	15,179,930
Balance at Mar. 31, 2017	$ 152	212,366	397,831	65,501	875	676,725
Balance (in shares) at Dec. 31, 2016	15,162,938
Balance at Dec. 31, 2016	$ 152	211,457	391,934	66,068		$ 669,611
Shares sold – options exercised (in shares)						48,995
Balance (in shares) at Dec. 31, 2017	15,212,133
Balance at Dec. 31, 2017	$ 152	215,659	419,423	67,504	694	$ 703,432
Net income (loss) attributable to National HealthCare Corporation			(2,791)			(2,791)
Net loss attributable to noncontrolling interest					(108)	(108)
Other comprehensive income (loss)				(2,219)		(2,219)
Stock–based compensation		428				$ 428
Shares sold – options exercised (in shares)	21,906					21,906
Shares sold – options exercised		1,067				$ 1,067
Dividends declared to common stockholders			(7,305)			(7,305)
Repurchase of common shares (in shares)	(14,506)
Repurchase of common shares		(867)				(867)
Balance (in shares) at Mar. 31, 2018	15,219,533
Balance at Mar. 31, 2018	$ 152	216,287	477,528	(2,916)	586	691,637
Reclassification due to new accounting standards			$ 68,201	$ (68,201)