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Summary of Significant Accounting Policies - Additional Information (Detail) | 9 Months Ended
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Sep. 30, 2015
Accounting Policies [Line Items] |
Cash and cash equivalents original maturities | 3 months
Minimum |
Accounting Policies [Line Items] |
Estimated useful lives of intangible assets | 4 years
Maximum |
Accounting Policies [Line Items] |
Estimated useful lives of intangible assets | 15 years

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- Definition Accounting policies. + References No definition available. + Details
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Namespace Prefix: | nk_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Cash and cash equivalents original maturities. + References No definition available. + Details
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Namespace Prefix: | nk_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |