Additional number of common shares reserved for future issuance.

No definition available.

Name:	ntra_CommonStockAdditionalCapitalSharesReservedForFutureIssuance
Namespace Prefix:	ntra_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the period after a contractual event that the entity's repurchase right expires.

+ References

No definition available.

+ Details

Name:	ntra_RepurchaseRightsExpirationPeriodAfterContractualEvent
Namespace Prefix:	ntra_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of shares exercised and unvested under the plan.

+ References

No definition available.

+ Details

Name:	ntra_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisedAndUnvested
Namespace Prefix:	ntra_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.29)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
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

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

- Details

Name:	us-gaap_PlanNameAxis=ntra_StockPlan2007Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=ntra_StockPlan2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=ntra_EmployeeAndNonEmployeeOptionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stock‑Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Stock‑Based Compensation (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015
Stock Based Compensation
Stock based compensation expense	$ 2,166	$ 1,065
2007 Plan
Stock Based Compensation
Shares reserved for issuance	15,999,289		15,999,289
2015 Plan
Stock Based Compensation
Shares reserved for issuance					3,451,495
Additional shares reserved for issuance					9,890,310
Employee and non-employee stock options
Stock Based Compensation
Stock based compensation expense			$ 4,906	$ 4,092
Employee and non-employee stock options \| 2007 Plan
Stock Based Compensation
Shares exercised and unvested	1,400,000
Period after Market Stand-off repurchase right expires	210 days
Stock based compensation expense	$ 600