XML 55 R43.htm IDEA: XBRL DOCUMENT
v3.25.3

Reinsurance - Schedule of the Inception Date, Covered Production Period, Contractual and Optional Termination Dates, Current Cession Rate, Ceding Commission and Profit Commission for Each Outstanding QSR Transaction (Details) - Third-party Reinsurers | 9 Months Ended
--- | ---
Sep. 30, 2025
Reinsurance Policy, Type [Axis]: 2018 QSR Transaction |
Ceded Credit Risk [Line Items] |
Ceding Commission | 20.00%
Profit Commission | 0.61
Reinsurance Policy, Type [Axis]: 2018 QSR Transaction, Period 1 |
Ceded Credit Risk [Line Items] |
Ceding percentage | 21.00%
Reinsurance Policy, Type [Axis]: 2018 QSR Transaction, Period 2 |
Ceded Credit Risk [Line Items] |
Ceding percentage | 17.00%
Reinsurance Policy, Type [Axis]: 2020 QSR Transaction |
Ceded Credit Risk [Line Items] |
Ceding percentage | 21.00%
Ceding Commission | 36.00%
Profit Commission | 0.50
Reinsurance Policy, Type [Axis]: 2021 QSR Transaction |
Ceded Credit Risk [Line Items] |
Ceding percentage | 20.00%
Ceding Commission | 35.00%
Profit Commission | 0.54
Reinsurance Policy, Type [Axis]: 2022 QSR Transaction |
Ceded Credit Risk [Line Items] |
Ceding percentage | 20.00%
Ceding Commission | 20.00%
Profit Commission | 0.62
Reinsurance Policy, Type [Axis]: 2022 Seasoned QSR Transaction |
Ceded Credit Risk [Line Items] |
Ceding percentage | 95.00%
Ceding Commission | 35.00%
Profit Commission | 0.55
Reinsurance Policy, Type [Axis]: 2023 QSR Transaction |
Ceded Credit Risk [Line Items] |
Ceding percentage | 20.00%
Ceding Commission | 20.00%
Profit Commission | 0.62
Reinsurance Policy, Type [Axis]: 2024 QSR Transaction |
Ceded Credit Risk [Line Items] |
Ceding percentage | 20.00%
Ceding Commission | 20.00%
Profit Commission | 0.56
Reinsurance Policy, Type [Axis]: 2025 QSR Transaction |
Ceded Credit Risk [Line Items] |
Ceding percentage | 20.00%
Ceding Commission | 20.00%
Profit Commission | 0.62
Reinsurance Policy, Type [Axis]: 2026 QSR Transactions |
Ceded Credit Risk [Line Items] |
Ceding percentage | 20.00%
Reinsurance Policy, Type [Axis]: 2027 QSR Transactions |
Ceded Credit Risk [Line Items] |
Ceding percentage | 12.00%

X
- Definition Ceded Credit Risk, Commission Earned, Percentage + References No definition available. + Details
Name: | nmih_CededCreditRiskCommissionEarnedPercentage
Namespace Prefix: | nmih_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Ceded Credit Risk, Profit Commission, Earned, Percentage + References No definition available. + Details
Name: | nmih_CededCreditRiskProfitCommissionEarnedPercentage
Namespace Prefix: | nmih_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Premiums Earned, Percent Of Risk + References No definition available. + Details
Name: | nmih_PremiumsEarnedPercentOfRisk
Namespace Prefix: | nmih_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 825 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477351/944-825-50-1B Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 825 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477351/944-825-50-1B + Details
Name: | us-gaap_CededCreditRiskLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_CededCreditRiskAxis=nmih_ThirdPartyReinsurersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2018 QSR Transaction
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2018 QSR Transaction, Period 1
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2018 QSR Transaction, Period 2
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2020 QSR Transaction
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2021 QSR Transaction
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2022 QSR Transaction
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2022 Seasoned QSR Transaction
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2023 QSR Transaction
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2024 QSR Transaction
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2025 QSR Transaction
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2026 QSR Transactions
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsuranceContractAxis=2027 QSR Transactions
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |