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v3.21.1

Revenue Recognition (Narrative) (Details) | 3 Months Ended
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Mar. 31, 2021
Revenue from Contract with Customer [Abstract] |
Service Area By County | 20

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- Definition Service Area By County + References No definition available. + Details
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Namespace Prefix: | nix_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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