Note 16 - Income Taxes (Details Textual) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Effective Income Tax Rate Reconciliation, Percent, Total	53.60%	3.00%	4.60%	5.20%
Effective Income Tax Rate Reconciliation, Benefit Resulting from Expiration of Applicable Statute Limitations, Amount	$ 1,444,000	$ 2,234,000	$ 1,444,000	$ 2,234,000

Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to benefits resulting from expiration of applicable statute of limitations.

No definition available.

Name:	nhc_EffectiveIncomeTaxRateReconciliationBenefitResultingFromExpirationOfApplicableStatuteLimitationsAmount
Namespace Prefix:	nhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration