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

No definition available.

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

- Definition

Represents the amount recognized in earnings during the period for the termination of a defined benefit plan.

+ References

No definition available.

+ Details

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Namespace Prefix:	sgc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Defined benefit plans number of plans

+ References

No definition available.

+ Details

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Namespace Prefix:	sgc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Defined benefit plans retirement age

+ References

No definition available.

+ Details

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Namespace Prefix:	sgc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of payment, which decreases benefit obligation of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract. Excludes decreases to benefit obligation for remeasurement due to settlement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(10)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Sum of the amount of expected guaranteed benefits in excess of the projected account balances for minimum guaranteed benefit contracts, as of the balance sheet date, net of reinsurance recoverables, for all guaranteed benefit types.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=124504833&loc=d3e7104-158389

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 80
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124508989&loc=d3e19393-158473

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_GuaranteedInsuranceContractTypeOfBenefitAxis=us-gaap_AnnuitizationBenefitMember
Namespace Prefix:
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Period Type:

Note 4 - Periodic Pension Expense (Details Textual) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2021 USD ($)	Mar. 31, 2021	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)
Defined Benefit Plans Number of Plans		2
Defined Benefit Plans Retirement Age (Year)		65 years
Defined Benefit Plan, Termination Charge	$ 6,945		$ 0	$ 6,945	$ 0
Noncontributory Qualified Defined Pension Plans [Member]
Defined Benefit Plan, Benefit Obligation, Payment for Settlement	13,800
Defined Benefit Plan, Termination Charge	6,900			6,900
Defined Benefit Plan, Remaining Undistributed Asset Surplus	1,300			1,300
Noncontributory Qualified Defined Pension Plans [Member] \| Annuitization Benefit [Member]
Guaranteed Benefit Liability, Net, Ending Balance	$ 3,000			$ 3,000