Face (par) amount of debt instrument at time of issuance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=nh_ConvertibleDebtRelatedPartyMember
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Fair Value Measurements - Fair Value of Debt (Details) - Convertible Debt - USD ($)	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2016	Dec. 21, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Face Value	$ 107,000,000	$ 107,000,000	$ 107,000,000	$ 107,000,000
Interest rate on debt			5.50%	5.50%
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	95,465,000	71,984,000
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	96,647,000	93,512,000
Related Party
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Face Value	10,000,000	10,000,000	$ 10,000
Related Party \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 8,922,000	6,727,000
Interest rate on debt	5.50%
Related Party \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 9,129,000	8,864,000
Others
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Face Value	97,000,000	97,000,000
Others \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	86,543,000	65,257,000
Others \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value	$ 87,518,000	$ 84,648,000