Long-term Debt - Schedule of long-term debt (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Less discount	$ (9,309)	$ (8,381)
Long-term debt	267,189	120,545
Securitized notes payable
Debt Instrument [Line Items]
Long-term debt, gross	54,996	0
Securitized notes payable \| NER 16-1 Class A-2 notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 19,975	0
Issue Date	2016
Stated Maturity Date	2021
Interest Rate	2.20%
Securitized notes payable \| NER 16-1 Class B notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 25,489	0
Issue Date	2016
Stated Maturity Date	2021
Interest Rate	3.22%
Securitized notes payable \| NER 16-1 Class C notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 6,319	0
Issue Date	2016
Stated Maturity Date	2021
Interest Rate	5.05%
Securitized notes payable \| NER 16-1 Class D notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 3,213	0
Issue Date	2016
Stated Maturity Date	2023
Interest Rate	7.87%
Senior debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 85,000	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	5.00%
Variable rate basis	3-month LIBOR
Senior debentures \| 2022 senior debentures \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	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	5.50%
Variable rate basis	3-month LIBOR
Senior debentures \| 2027 senior debentures \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	3.71%
Subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 111,500	11,500
Subordinated debentures \| 2028 subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000	0
Issue Date	2018
Stated Maturity Date	2028
Earliest Call Date	2023
Interest Rate	4.50%
Variable rate basis	3-month LIBOR
Subordinated debentures \| 2028 subordinated debentures \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	2.12%
Subordinated debentures \| 2025 subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 11,500	11,500
Issue Date	2015
Stated Maturity Date	2025
Earliest Call Date	2020
Interest Rate	6.25%
Trust preferred securities
Debt Instrument [Line Items]
Long-term debt, gross	$ 25,002	32,426
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
Variable rate basis	Prime
Trust preferred securities \| Southern Bancorp Capital Trust I \| Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Trust preferred securities \| United Community Statutory Trust III
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	1,238
Issue Date	2008
Stated Maturity Date	2038
Earliest Call Date	2013
Variable rate basis	Prime
Trust preferred securities \| United Community Statutory Trust III \| Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate	3.00%
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
Variable rate basis	3-month LIBOR
Trust preferred securities \| Tidelands Statutory Trust I \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.38%
Trust preferred securities \| Tidelands Statutory Trust II
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	6,186
Issue Date	2008
Stated Maturity Date	2038
Earliest Call Date	2013
Variable rate basis	3-month LIBOR
Trust preferred securities \| Tidelands Statutory Trust II \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	5.075%
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
Variable rate basis	3-month LIBOR
Trust preferred securities \| Four Oaks Statutory Trust I \| LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate	1.35%

This element represents debt instrument earliest call year.

No definition available.

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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

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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

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Namespace Prefix:	ucbi_
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Balance Type:	na
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- Definition

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

+ References

No definition available.

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- 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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Period Type:	instant

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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- Definition

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

+ References

+ Details

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- 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

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- Definition

Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

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+ Details

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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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
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Period Type:	instant

- Details

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