Note 6 - Share-based Compensation - Stock-settled Stock Appreciation Rights Transactions (Details) - Stock Appreciation Rights (SARs) [Member] - $ / shares	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Outstanding SARS (in shares)			146,504
Outstanding SARS, weighted average exercise price (in dollars per share)			$ 17.38
Granted SARS (in shares)			48,515	43,988
Granted SARS, weighted average exercise price (in dollars per share)			$ 23.59
Exercised SARS (in shares)	0	(68,698)	(12,125)	(128,062)
Exercised SARS, weighted average exercise price (in dollars per share)			$ 17.92
Outstanding SARS (in shares)	182,894		182,894
Outstanding SARS, weighted average exercise price (in dollars per share)	$ 18.99		$ 18.99

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

The weighted average grant-date fair value of SARS exercised during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

No definition available.

+ Details

Name:	sgc_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsExercisedInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	sgc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average exercise price of non-option equity instruments granted during the period.

+ References

No definition available.

+ Details

Name:	sgc_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	sgc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of non-option equity instruments exercised by participants.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Net number of non-option equity instruments granted to participants.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
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://fasb.org/us-gaap/role/ref/legacyRef
-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=109197908&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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=109197908&loc=d3e5070-113901

+ Details

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

- Details

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