Percentage, before allowance for credit loss, of financing receivable to total financing receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

+ Details

Name:	srt_FinancingReceivableBeforeAllowanceForCreditLossToTotalPercent
Namespace Prefix:	srt_
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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 40
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481628/310-20-40-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

+ Details

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

- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

+ Details

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

- Definition

Amortized cost excluding accrued interest, after allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

+ Details

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

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_CommercialRealEstateNonOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_ConstructionLandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_CommercialRealEstateOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_CommercialAndIndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_PinnaclePublicFinanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_BridgeFranchiseAndEquipmentFinanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_MortgagewarehouselendingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_A14SingleFamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_GovernmentInsuredResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Allowance for Credit Losses (Schedule of Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 23,933,527		$ 24,297,980
Allowance for credit losses	(222,730)	$ (219,747)	(223,153)	$ (225,698)	$ (217,556)	$ (202,689)
Loans, net	$ 23,710,797		$ 24,074,827
Percent of Total Loans	100.00%		100.00%
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 16,629,530		$ 16,717,166
Allowance for credit losses	$ (208,961)	(204,180)	$ (211,203)	(219,472)	(210,929)	(195,058)
Percent of Total Loans	69.50%		68.80%
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 7,303,997		$ 7,580,814
Allowance for credit losses	$ (13,769)	$ (15,567)	$ (11,950)	$ (6,226)	$ (6,627)	$ (7,631)
Percent of Total Loans	30.50%		31.20%
Non-owner occupied commercial real estate \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 5,829,835		$ 5,652,203
Percent of Total Loans	24.40%		23.30%
Construction and land \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 643,630		$ 561,989
Percent of Total Loans	2.70%		2.30%
Owner occupied commercial real estate \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 1,942,076		$ 1,941,004
Percent of Total Loans	8.10%		8.00%
Commercial and industrial \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,743,739		$ 7,042,222
Percent of Total Loans	28.20%		28.90%
Pinnacle - municipal finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 694,639		$ 720,661
Pinnacle - municipal finance \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 694,639		$ 720,661
Percent of Total Loans	2.90%		3.00%
Franchise and equipment finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 149,022		$ 213,477
Franchise and equipment finance \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 149,022		$ 213,477
Percent of Total Loans	0.60%		0.90%
Mortgage warehouse lending
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 626,589		$ 585,610
Mortgage warehouse lending \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 626,589		$ 585,610
Percent of Total Loans	2.60%		2.40%
1-4 single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,310,932		$ 6,508,922
1-4 single family residential \| Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,310,932		$ 6,508,922
Percent of Total Loans	26.40%		26.80%
Government insured residential \| Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 993,065		$ 1,071,892
Percent of Total Loans	4.10%		4.40%