Note 4 - Periodic Pension Expense (Details Textual) $ in Millions	3 Months Ended
Mar. 31, 2022 USD ($) yr
Defined Benefit Plans Number of Plans	2
Defined Benefit Plans Retirement Age (Year) \| yr	65
Noncontributory Qualified Defined Pension Plans [Member]
Defined Benefit Plan, Remaining Undistributed Asset Surplus \| $	$ 0.4

Represents the amount of remaining undistributed asset surplus under a defined benefit plan.

No definition available.

Name:	sgc_DefinedBenefitPlanRemainingUndistributedAssetSurplus
Namespace Prefix:	sgc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant