Debt instrument number of loan agreement.

No definition available.

Name:	stg_DebtInstrumentNumberOfLoanAgreement
Namespace Prefix:	stg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of assets pledged to secure a debt instrument.

+ References

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+ Details

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

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+ Details

Name:	us-gaap_DebtInstrumentFrequencyOfPeriodicPayment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

+ References

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+ Details

Name:	us-gaap_RepaymentsOfSecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=stg_PRCBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt - Additional Information (Details) ¥ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2021 CNY (¥)	Dec. 31, 2021 CNY (¥)	Dec. 31, 2020 CNY (¥)	Dec. 31, 2019 CNY (¥)	Apr. 14, 2021	Nov. 21, 2018 CNY (¥) Loan	Aug. 29, 2018 CNY (¥) Loan
Debt Instrument [Line Items]
Debt instrument, term	10 years	8 years
Mortgage Bank Loan
Debt Instrument [Line Items]
Debt instrument, face amount		¥ 321,540
Mortgage Bank Loan \| PRC Bank
Debt Instrument [Line Items]
Debt instrument number of loan agreement \| Loan						2	2
Debt instrument, face amount	¥ 61,540					¥ 260,000	¥ 260,000
Debt instrument periodic payment description	The loan is secured by pledging Building B and is repaid in equal instalment every three months with maturity term of 10 years.	The loans are secured by pledging Building A and Building D and are repaid in equal instalment every three months with maturity term of 8 years.
Debt instrument, interest rate	1.05%	1.25%			1.472%
Repayment of secured loans		¥ 34,038	¥ 32,500	¥ 32,500
Debt instrument, security deposit		¥ 50,008