3) Investments: Summary of Interest not accrued on non-performing mortgage loans (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Text Block [Abstract]
Interest not accrued on non-performing loans	$ 321,000	$ 491,000

Represents the monetary amount of Interest not accrued on non-performing loans, as of the indicated date.

No definition available.

Name:	snfc_InterestNotAccruedOnNonPerformingLoans
Namespace Prefix:	snfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant