v3.6.0.2

Fair Value Measurements - Assumptions (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) company	Dec. 31, 2015 company
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Volatility, basket of companies | company	4	15
Warrants
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Warrants	$ 3,792
Volatility (as a percent)	61.30%
Warrant valuation increase	$ 100

X

- Definition

Represents increase in the warrant valuation resulting from change in the volatility assumption.

+ References

No definition available.

+ Details

Name:	ntra_ClassOfWarrantOrRightWarrantValuationIncrease
Namespace Prefix:	ntra_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Represents the number of companies considered from a basket comparison in regards to the volatility assumption.

+ References

No definition available.

+ Details

Name:	ntra_VolatilityAssumptionBasketComparisonNumberOfCompanies
Namespace Prefix:	ntra_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssumptionsExpectedVolatilityRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- 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

Name:	us-gaap_FairValueInputsLiabilitiesQuantitativeInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Fair value portion of warrants not settleable in cash classified as equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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

X

- Details

Name:	us-gaap_ShareholdersEquityClassAxis=us-gaap_WarrantsNotSettleableInCashMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: