Note 6 - Share-based Compensation - Stock Appreciation Rights Outstanding (Details) - $ / shares	9 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Lower range of exercise prices on options (in dollars per share)	$ 3.82
Upper range of exercise prices on options (in dollars per share)	21.63
Stock Appreciation Rights (SARs) [Member]
Lower range of exercise prices on options (in dollars per share)	5.65
Upper range of exercise prices on options (in dollars per share)	$ 21.63
Outstanding SARs (in shares)	241,432	325,506
Weighted average remaining contractual life (Year)	2 years 127 days
Weighted average exercise price (in dollars per share)	$ 13.28	$ 10.26
Exercise Price Range 1 [Member]
Lower range of exercise prices on options (in dollars per share)	3.82
Upper range of exercise prices on options (in dollars per share)	5.55
Exercise Price Range 1 [Member] \| Stock Appreciation Rights (SARs) [Member]
Lower range of exercise prices on options (in dollars per share)	5.65
Upper range of exercise prices on options (in dollars per share)	$ 7.36
Outstanding SARs (in shares)	94,928
Weighted average remaining contractual life (Year)	1 year 32 days
Weighted average exercise price (in dollars per share)	$ 6.95
Exercise Price Range 2 [Member]
Lower range of exercise prices on options (in dollars per share)	5.65
Upper range of exercise prices on options (in dollars per share)	7.36
Exercise Price Range 2 [Member] \| Stock Appreciation Rights (SARs) [Member]
Lower range of exercise prices on options (in dollars per share)	16.35
Upper range of exercise prices on options (in dollars per share)	$ 21.63
Outstanding SARs (in shares)	146,504
Weighted average remaining contractual life (Year)	3 years 62 days
Weighted average exercise price (in dollars per share)	$ 17.38

The weighted average exercise price for non-option equity instruments.

No definition available.

Name:	sgc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsNonOptionOutstandingWeightedAverageGrantDateFairValue
Namespace Prefix:	sgc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_StockAppreciationRightsSARSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=sgc_ExercisePriceRangeOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=sgc_ExercisePriceRangeTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: