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Note 2 - Revenue (Details Textual) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Revenue from Contract with Customers, Sales Returns, Percent | 1.00% | 2.00%
Contract with Customer, Liability, Revenue Recognized | $ 1.4 |
Minimum [Member] |  |
Revenue from Contract with Customer, Sales Returns Policy Term (Day) | 14 days |
Revenue from Contract with Customers, Historical Sales Returns, Percent | 1.00% |
Maximum [Member] |  |
Revenue from Contract with Customer, Sales Returns Policy Term (Day) | 1 year |
Revenue from Contract with Customers, Historical Sales Returns, Percent | 10.00% |

X
- Definition Represents the sales returns policy term. + References No definition available. + Details
Name: | nhtc_RevenueFromContractWithCustomerSalesReturnsPolicyTerm
Namespace Prefix: | nhtc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the percentage of historical sales returns. + References No definition available. + Details
Name: | nhtc_RevenueFromContractWithCustomersHistoricalSalesReturnsPercent
Namespace Prefix: | nhtc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the percentage of sales returns. + References No definition available. + Details
Name: | nhtc_RevenueFromContractWithCustomersSalesReturnsPercent
Namespace Prefix: | nhtc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045 + Details
Name: | us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |