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, 2017	15,212,133
Balance at Dec. 31, 2017	$ 152	$ 215,659	$ 419,423	$ 67,504	$ 694	$ 703,432
Net income attributable to National HealthCare Corporation	0	0	(2,791)	0	0	(2,791)
Net loss attributable to noncontrolling interest	0	0	0	0	(108)	(108)
Other comprehensive income (loss)	0	0	0	(2,219)	0	(2,219)
Stock–based compensation	$ 0	428	0	0	0	428
Shares sold – options exercised (in shares)	21,906
Shares sold – options exercised	$ 0	1,067	0	0	0	1,067
Repurchase of common shares (in shares)	(14,506)
Repurchase of common shares	$ 0	(867)	0	0	0	(867)
Dividends declared to common stockholders	$ 0	0	(7,305)	0	0	(7,305)
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 at Dec. 31, 2017	$ 0	0	68,201	(68,201)	0	0
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 attributable to National HealthCare Corporation						40,812
Net loss attributable to noncontrolling interest						(249)
Other comprehensive income (loss)						(2,995)
Balance (in shares) at Sep. 30, 2018	15,225,654
Balance at Sep. 30, 2018	$ 152	217,657	505,906	(3,692)	1,195	721,218
Reclassification due to new accounting standards at Dec. 31, 2017	$ 0	0	68,201	(68,201)	0	0
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
Shares sold – options exercised (in shares)						68,291
Balance (in shares) at Dec. 31, 2018	15,255,002
Balance at Dec. 31, 2018	$ 153	219,435	516,435	(2,745)	1,179	$ 734,457
Reclassification due to new accounting standards at Dec. 31, 2017	$ 0	0	68,201	(68,201)	0	0
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
Net income attributable to National HealthCare Corporation	0	0	22,461	0	0	22,461
Net loss attributable to noncontrolling interest	0	0	0	0	(86)	(86)
Other comprehensive income (loss)	0	0	0	(639)	0	(639)
Stock–based compensation	$ 0	749	0	0	0	749
Shares sold – options exercised (in shares)	6,121
Shares sold – options exercised	$ 0	260	0	0	0	260
Dividends declared to common stockholders	$ 0	0	(7,612)	0	0	(7,612)
Balance (in shares) at Jun. 30, 2018	15,225,654
Balance at Jun. 30, 2018	$ 152	217,296	492,377	(3,555)	500	706,770
Net income attributable to National HealthCare Corporation	0	0	21,142	0	0	21,142
Net loss attributable to noncontrolling interest	0	0	0	0	(55)	(55)
Other comprehensive income (loss)	0	0	0	(137)	0	(137)
Stock–based compensation	0	361	0	0	0	361
Dividends declared to common stockholders	$ 0	0	(7,613)	0	0	(7,613)
Balance (in shares) at Sep. 30, 2018	15,225,654
Balance at Sep. 30, 2018	$ 152	217,657	505,906	(3,692)	1,195	721,218
Equity contributed by noncontrolling interest					750	750
Balance (in shares) at Dec. 31, 2018	15,255,002
Balance at Dec. 31, 2018	$ 153	219,435	516,435	(2,745)	1,179	734,457
Net income attributable to National HealthCare Corporation	0	0	21,269	0	0	21,269
Net loss attributable to noncontrolling interest	0	0	0	0	(38)	(38)
Other comprehensive income (loss)	0	0	0	2,548	0	2,548
Stock–based compensation	$ 0	424	0	0	0	424
Shares sold – options exercised (in shares)	59,384
Shares sold – options exercised	$ 0	579	0	0	0	579
Repurchase of common shares (in shares)	(10,396)
Repurchase of common shares	$ 0	(872)	0	0	0	(872)
Dividends declared to common stockholders	$ 0	0	(7,652)	0	0	(7,652)
Balance (in shares) at Mar. 31, 2019	15,303,990
Balance at Mar. 31, 2019	$ 153	219,566	530,052	(197)	1,141	750,715
Balance (in shares) at Dec. 31, 2018	15,255,002
Balance at Dec. 31, 2018	$ 153	219,435	516,435	(2,745)	1,179	734,457
Net income attributable to National HealthCare Corporation						54,441
Net loss attributable to noncontrolling interest						(152)
Other comprehensive income (loss)						$ 5,476
Shares sold – options exercised (in shares)						332,852
Balance (in shares) at Sep. 30, 2019	15,318,790
Balance at Sep. 30, 2019	$ 153	221,394	547,292	2,731	461	$ 772,031
Balance (in shares) at Mar. 31, 2019	15,303,990
Balance at Mar. 31, 2019	$ 153	219,566	530,052	(197)	1,141	750,715
Net income attributable to National HealthCare Corporation	0	0	13,711	0	0	13,711
Net loss attributable to noncontrolling interest	0	0	0	0	(29)	(29)
Other comprehensive income (loss)	0	0	0	2,345	0	2,345
Stock–based compensation	$ 0	684	0	0	0	684
Shares sold – options exercised (in shares)	14,800
Shares sold – options exercised	$ 0	804	0	0	0	804
Dividends declared to common stockholders	0	0	(7,966)	0	0	(7,966)
Distributions attributable to noncontrolling interest	$ 0	0	0	0	(17)	(17)
Balance (in shares) at Jun. 30, 2019	15,318,790
Balance at Jun. 30, 2019	$ 153	221,054	535,797	2,148	1,095	760,247
Net income attributable to National HealthCare Corporation	0	0	19,461	0	0	19,461
Net loss attributable to noncontrolling interest	0	0	0	0	(85)	(85)
Other comprehensive income (loss)	0	0	0	583	0	583
Stock–based compensation	0	340	0	0	0	340
Dividends declared to common stockholders	0	0	(7,966)	0	0	(7,966)
Distributions attributable to noncontrolling interest	$ 0	0	0	0	(549)	(549)
Balance (in shares) at Sep. 30, 2019	15,318,790
Balance at Sep. 30, 2019	$ 153	$ 221,394	$ 547,292	$ 2,731	$ 461	$ 772,031