No definition available.

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

- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the best estimate at the acquisition date of the contractual cash flows not expected to be collected, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

+ Details

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

- Definition

Fair value of acquired receivable from business combination, excluding certain loans and debt securities acquired in transfer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

+ Details

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

- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the gross contractual amounts receivable, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Fair value at acquisition of acquired loans accounted for as held-to-maturity debt securities with evidence of deterioration of credit quality.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

+ Details

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

- Definition

Amount of cash flows expected to be collected at acquisition of acquired loans accounted for as held-to-maturity debt securities with evidence of deterioration of credit quality.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 15
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82894507&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

+ Details

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

- Definition

Amount of contractually required payments receivable at acquisition of acquired loans accounted for as held-to-maturity debt securities with evidence of deterioration of credit quality.

+ References

+ Details

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

- Definition

The aggregate excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan. This relates to loans with deteriorating of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

No definition available.

+ Details

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

- Definition

The amount of the loan's contractually required payments receivable in excess of the amount of its cash flows expected to be collected. This relates to loans with deteriorating of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ucbi_NLFCHoldingsCorpAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ucbi_FourOaksFinCorpIncAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ucbi_HCSBFinancialCorporationAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=ucbi_TidelandsBancsharesIncAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Mergers and Acquisitions - Acquired loan and lease asset portfolio at acquisition date (Details) - USD ($) $ in Thousands	Feb. 01, 2018	Nov. 01, 2017	Jul. 31, 2017	Jul. 01, 2016
NLFC Holdings Corp
Accounted for pursuant to ASC 310-30
Contractually required principal and interest	$ 24,711
Non-accretable difference	5,505
Cash flows expected to be collected	19,206
Accretable yield	1,977
Fair value	17,229
Excluded from ASC 310-30
Fair value	341,123
Gross contractual amounts receivable	389,432
Estimate of contractual cash flows not expected to be collected	$ 8,624
Four Oaks FinCorp, Inc
Accounted for pursuant to ASC 310-30
Contractually required principal and interest		$ 49,377
Non-accretable difference		8,244
Cash flows expected to be collected		41,133
Accretable yield		3,313
Fair value		37,820
Excluded from ASC 310-30
Fair value		448,462
Gross contractual amounts receivable		509,629
Estimate of contractual cash flows not expected to be collected		$ 6,081
HCSB Financial Corporation
Accounted for pursuant to ASC 310-30
Contractually required principal and interest			$ 46,069
Non-accretable difference			12,413
Cash flows expected to be collected			33,656
Accretable yield			3,410
Fair value			30,246
Excluded from ASC 310-30
Fair value			185,701
Gross contractual amounts receivable			212,780
Estimate of contractual cash flows not expected to be collected			$ 3,985
Tidelands Bancshares, Inc
Accounted for pursuant to ASC 310-30
Contractually required principal and interest				$ 50,660
Non-accretable difference				13,483
Cash flows expected to be collected				37,177
Accretable yield				2,113
Fair value				35,064
Excluded from ASC 310-30
Fair value				270,839
Gross contractual amounts receivable				302,331
Estimate of contractual cash flows not expected to be collected				$ 3,859