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Regulatory Matters (Narrative) (Details) $ in Millions | Sep. 30, 2021 USD ($)
--- | ---
Regulated Operations [Abstract] |
Columbia of Maryland COVID Relief Funds | $ 0.8

X
- Definition Columbia of Maryland COVID Relief Funds + References No definition available. + Details
Name: | nix_ColumbiaOfMarylandCOVIDReliefFunds
Namespace Prefix: | nix_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_RegulatedOperationsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration