3) Investments (Details)	Sep. 30, 2020	Dec. 31, 2019
Text Block [Abstract]
Average market value over amortized cost	93.50%	98.90%

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

No definition available.

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