Loan Servicing, Mortgage Origination, and Loans Held for Sale - Mandatory cash forwards (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Mortgage loan securitizations, mandatory cash forwards, and whole loan sales
Loan sales	$ 228,300	$ 115,300
Loan securitizations and loan sales	$ 194,500	$ 89,100
Percentage of loan securitizations and loan sales	85.20%	77.30%
Loans held for sale	$ 71,719	$ 33,297	$ 59,363
Residential mortgage loans to be sold in secondary market
Mortgage loan securitizations, mandatory cash forwards, and whole loan sales
Loans held for sale	$ 71,700	$ 33,300	$ 59,400
Residential mortgage loans awaiting sale in secondary market \| Minimum
Mortgage loan securitizations, mandatory cash forwards, and whole loan sales
Loans held for sale, settlement period	15 days
Residential mortgage loans awaiting sale in secondary market \| Maximum
Mortgage loan securitizations, mandatory cash forwards, and whole loan sales
Loans held for sale, settlement period	45 days

Represent the settlement period of loan held for sale.

No definition available.

Name:	ssb_LoansHeldForSaleSettlementPeriod
Namespace Prefix:	ssb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of mortgage loan securitized and sold during the period.

+ References

No definition available.

+ Details

Name:	ssb_MortgageLoanSecuritizationsAndSales
Namespace Prefix:	ssb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	ssb_MortgageLoanSecuritizationsAndSalesAbstract
Namespace Prefix:	ssb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of mortgage loan sold during the period.

+ References

No definition available.

+ Details

Name:	ssb_MortgageLoanSold
Namespace Prefix:	ssb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the percentage of mortgage loan securitized and sold during the period with servicing rights retained by the company.

+ References

No definition available.

+ Details

Name:	ssb_PercentageOfMortgageLoanSecuritizationsAndSales
Namespace Prefix:	ssb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=ssb_ResidentialMortgageLoansToBeSoldInSecondaryMarketMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=ssb_ResidentialMortgageLoansAwaitingSaleInSecondaryMarketMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
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