12) Mortgage Servicing Rights: Summary of Unpaid Principal Balances of the Servicing Portfolio (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Text Block [Abstract]
Servicing Unpaid Principal Balance	$ 2,820,985,128	$ 2,804,139,415

Represents the monetary amount of Servicing Unpaid Principal Balance, as of the indicated date.

No definition available.

Name:	snfc_ServicingUnpaidPrincipalBalance
Namespace Prefix:	snfc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant