This element represents debt instrument earliest call year.

No definition available.

Name:	ucbi_DebtInstrumentEarliestCallYear
Namespace Prefix:	ucbi_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents debt instrument issue year.

+ References

No definition available.

+ Details

Name:	ucbi_DebtInstrumentIssueYear
Namespace Prefix:	ucbi_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents debt instruments maturity year.

+ References

No definition available.

+ Details

Name:	ucbi_DebtInstrumentsMaturityYear
Namespace Prefix:	ucbi_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num: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

Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28541-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=ucbi_TwoThousandTwentyTwoSeniorDebenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ucbi_TwoThousandTwentySevenSeniorDebenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ucbi_TwoThousandThirtySeniorDebenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=ucbi_TwoThousandTwentySixSubordinatedDebenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ucbi_TwoThousandTwentyEightSubordinatedDebenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ucbi_TwoThousandTwentyFiveSubordinatedDebenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=ucbi_SouthernBancorpCapitalTrustOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ucbi_TidelandsStatutoryTrustOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ucbi_FourOaksStatutoryTrustIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-term Debt - Schedule of long-term debt (Details) - USD ($) $ in Thousands	9 Months Ended	29 Months Ended		67 Months Ended	71 Months Ended
	Sep. 30, 2020	Dec. 31, 2027	Dec. 31, 2022	Dec. 31, 2030	Dec. 31, 2028	Dec. 31, 2019
Debt Instrument [Line Items]
Less discount	$ (9,549)					$ (8,588)
Total long-term debt	326,703					212,664
Senior debentures
Debt Instrument [Line Items]
Long-term debt, gross	185,000					85,000
Senior debentures \| 2022 senior debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 50,000					50,000
Issue Date	2015
Stated Maturity Date	2022
Earliest Call Date	2020
Interest Rate (percent)	5.00%
Senior debentures \| 2022 senior debentures \| LIBOR \| Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (spread)			3.814%
Senior debentures \| 2027 senior debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 35,000					35,000
Issue Date	2015
Stated Maturity Date	2027
Earliest Call Date	2025
Interest Rate (percent)	5.50%
Senior debentures \| 2027 senior debentures \| LIBOR \| Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (spread)		3.71%
Senior debentures \| 2030 senior debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000					0
Issue Date	2020
Stated Maturity Date	2030
Earliest Call Date	2025
Interest Rate (percent)	5.00%
Senior debentures \| 2030 senior debentures \| SOFR \| Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (spread)				4.87%
Subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 111,250					111,250
Subordinated debentures \| 2026 subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 15,000					0
Issue Date	2016
Stated Maturity Date	2026
Earliest Call Date	2021
Interest Rate (percent)	5.875%
Subordinated debentures \| 2026 subordinated debentures \| LIBOR \| Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (spread)					4.70%
Subordinated debentures \| 2028 subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000					100,000
Issue Date	2018
Stated Maturity Date	2028
Earliest Call Date	2023
Interest Rate (percent)	4.50%
Subordinated debentures \| 2028 subordinated debentures \| LIBOR \| Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (spread)					2.12%
Subordinated debentures \| 2025 subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 11,250					11,250
Issue Date	2015
Stated Maturity Date	2025
Earliest Call Date	2020
Interest Rate (percent)	6.25%
Trust preferred securities
Debt Instrument [Line Items]
Long-term debt, gross	$ 25,002					25,002
Trust preferred securities \| Southern Bancorp Capital Trust I
Debt Instrument [Line Items]
Long-term debt, gross	$ 4,382					4,382
Issue Date	2004
Stated Maturity Date	2034
Earliest Call Date	2009
Trust preferred securities \| Southern Bancorp Capital Trust I \| Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate (spread)	1.00%
Trust preferred securities \| Tidelands Statutory Trust I
Debt Instrument [Line Items]
Long-term debt, gross	$ 8,248					8,248
Issue Date	2006
Stated Maturity Date	2036
Earliest Call Date	2011
Trust preferred securities \| Tidelands Statutory Trust I \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (spread)	1.38%
Trust preferred securities \| Four Oaks Statutory Trust I
Debt Instrument [Line Items]
Long-term debt, gross	$ 12,372					$ 12,372
Issue Date	2006
Stated Maturity Date	2036
Earliest Call Date	2011
Basis spread on variable rate (spread)	1.35%