v3.19.3.a.u2

Summary of Significant Accounting Policies - Concentration (Details) - customer	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Sales | Customer
Risk and Uncertainties
Number of customers exceeding 10% of benchmark	0	0	0
Accounts receivable | Credit
Risk and Uncertainties
Number of customers exceeding 10% of benchmark	0	0

X

- Definition

Represents the number of customers.

+ References

No definition available.

+ Details

Name:	ntra_NumberOfCustomers
Namespace Prefix:	ntra_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AccountsReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CreditConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: