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3) Investments: Summary of Interest not accrued on non-performing mortgage loans (Details) - USD ($) | Sep. 30, 2020 | Dec. 31, 2019
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Text Block [Abstract] |  |
Interest not accrued on non-performing loans | $ 397,000 | $ 203,000

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- Definition Represents the monetary amount of Interest not accrued on non-performing loans, as of the indicated date. + References No definition available. + Details
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Namespace Prefix: | snfc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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