| **Summary of Significant Accounting Policies - Narrative (Details)**                            | 3 Months Ended |
|-------------------------------------------------------------------------------------------------|----------------|
||
| **Accounting Policies [Line Items]**                                                            |           |
| Number Of Segments                                                                              | 4              |
| Number Of Employees Hourly Workers [Member] | Unionized Employees Concentration Risk [Member]   |           |
| **Risks and Uncertainties [Abstract]**                                                          |           |
| Concentration Risk Number Of Employees                                                          | 4,600          |
| concentration risk number of employees percentage                                               | 49.00%         |
| Number of Employees Salaried Workers [Member] | Unionized Employees Concentration Risk [Member] |           |
| **Risks and Uncertainties [Abstract]**                                                          |           |
| Concentration Risk Number Of Employees                                                          | 400            |
| concentration risk number of employees percentage                                               | 5.00%          |

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| X                                                                                                                                                                                                                                                        |
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| - Definition
Concentration Risk Number Of Employees
+ References
No definition available.
+ Details**Name:**nav_ConcentrationRiskNumberOfEmployees**Namespace Prefix:**nav_**Data Type:**xbrli:decimalItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
concentration risk number of employees percentage
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
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| - Definition
Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.
+ References
No definition available.
+ Details**Name:**us-gaap_NumberOfReportableSegments**Namespace Prefix:**us-gaap_**Data Type:**xbrli:integerItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                 |
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