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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Feb. 28, 2010	Mar. 31, 2018
Accounting Policies [Line Items]
Variable consideration related to milestone payment		$ 0
Revenue recognized for milestone payment		$ 0
Intrexon Corporation
Accounting Policies [Line Items]
Nonrefundable upfront payment	$ 400

X

- Definition

Accounting policies.

+ References

No definition available.

+ Details

Name:	nk_AccountingPoliciesLineItems
Namespace Prefix:	nk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Nonrefundable upfront payment.

+ References

No definition available.

+ Details

Name:	nk_NonrefundableUpfrontPayment
Namespace Prefix:	nk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Revenue recognized for milestone payment.

+ References

No definition available.

+ Details

Name:	nk_RevenueRecognizedForMilestonePayment
Namespace Prefix:	nk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Variable consideration related to milestone payment.

+ References

No definition available.

+ Details

Name:	nk_VariableConsiderationRelatedToMilestonePayment
Namespace Prefix:	nk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=nk_IntrexonLicenseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: