Long-term Debt - Narrative (Details) - USD ($)	1 Months Ended	12 Months Ended
Jan. 31, 2018	Dec. 31, 2018
Senior debentures \| 2022 senior debentures
Debt Instrument [Line Items]
Percentage of principal amount redeemed		100.00%
Maturity date		Feb. 14, 2022
Senior debentures \| 2027 senior debentures
Debt Instrument [Line Items]
Percentage of principal amount redeemed		100.00%
Maturity date		Feb. 14, 2027
Subordinated debentures \| 2025 subordinated debentures
Debt Instrument [Line Items]
Maturity date		Nov. 30, 2025
Earliest date allowed for prepayment		Nov. 30, 2020
Aggregate principal amount		$ 11,500,000.0
Subordinated debentures \| 2028 subordinated debentures
Debt Instrument [Line Items]
Maturity date	Jan. 30, 2028
Aggregate principal amount	$ 100,000,000

Earliest date when the debt instrument can be prepaid, in CCYY-MM-DD format.

No definition available.

Name:	ucbi_DebtInstrumentPrepaymentEarliestDate
Namespace Prefix:	ucbi_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

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

- 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_DebtInstrumentAxis=ucbi_TwoThousandTwentySevenSeniorDebenturesMember
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_TwoThousandTwentyFiveSubordinatedDebenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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