Investment Securities (Details Narrative)	Mar. 31, 2018 Integer
Schedule of Investments [Abstract]
Available-for-sale securities, number of debt securities	89
Percentage of debt securities unrealized losses depreciated on amortized cost basis	2.50%

Percentage of debt securities unrealized losses depreciated on amortized cost basis.

No definition available.

Name:	SGB_PercentageOfDebtSecuritiesUnrealizedLossesDepreciatedOnAmortizedCostBasis
Namespace Prefix:	SGB_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant