Investment Securities - Additonal disclosures - (Details)	3 Months Ended	12 Months Ended
Sep. 30, 2017 USD ($) security	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)
Additional disclosures
Other-than-temporary impairment on securities	$ 753,000	$ 753,000	$ 489,000
Number of equity securities sold \| security	2
Carrying value of investment securities pledged to secure public funds deposits and for other purposes required and permitted by law		766,000,000		$ 295,200,000
Carrying amount of the securities pledged to collateralize repurchase agreements		$ 211,100,000		$ 238,300,000

Represents the number of equity securities sold during the period for which an impairment has been recorded.

No definition available.

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- References

No definition available.

+ Details

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- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for public funds deposits and for other purposes required and permitted by law, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

Name:	ssb_PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledgedForPublicFundsDepositsAndOtherPurposesRequiredAndPermittedByLaw
Namespace Prefix:	ssb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant