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3) Investments (Details)	Mar. 31, 2021	Dec. 31, 2020
Text Block [Abstract]
Average market value over amortized cost	97.30%	94.70%

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- Definition

Represents the Average market value over amortized cost, as of the indicated date.

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No definition available.

+ Details

Name:	snfc_AverageMarketValueOverAmortizedCost
Namespace Prefix:	snfc_
Data Type:	num:percentItemType
Balance Type:	na
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