Fair Value Measurements - Schedule of Change in the Fair Value of the Warrant Liability (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Beginning balance	$ 1,169	$ 213
Change in fair value of warrant liability	3,317	562
Conversion of preferred stock warrants to common stock warrants upon the closing of the IPO	$ (4,486)
Ending balance		$ 775

Fair value measurement with unobservable inputs reconciliation recurring basis liability conversion of preferred stock warrants to common stock warrants upon the closing of the IPO.

No definition available.

+ Details

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Namespace Prefix:	nari_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

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- Definition

Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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Period Type:	instant