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v3.19.1

Commitments and Contingencies (Details Textual) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2003
Commitments And Contingencies [Line Items] |  |  |  |
Rent expense | $ 1,603,000 | $ 1,558,000 | $ 1,519,000 |
Contingent cash payment |  |  |  | $ 1,000,000

X
- Definition Amount of potential cash payments that could result from the contingent consideration arrangement. + References No definition available. + Details
Name: | sga_BusinessAcquisitionContingentConsiderationPotentialCashPayments
Namespace Prefix: | sga_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | sga_CommitmentsAndContingenciesLineItems
Namespace Prefix: | sga_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
Name: | us-gaap_LeaseAndRentalExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration