Financing receivable credit quality indicator, the value at which relationships are reevaluated at least annually

No definition available.

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Amount of unpaid principal balance of ACI loans

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

The unpaid principal balance of pledged real estate loans.

+ References

No definition available.

+ Details

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- Definition

The net investment in direct financing leases as of the balance sheet date consisting of: (a) minimum lease payments due on direct financing leases, (b) unguaranteed residual value, and (c) any unamortized initial direct costs; less: (i) executory costs, (ii) unearned income, and (iii) the accumulated allowance for uncollectible minimum lease payments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84165051&loc=d3e45377-112738

+ 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 of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18794-111554

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL49126937-111524

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(4))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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Balance Type:	debit
Period Type:	instant

- Definition

The cash outflow associated with purchasing loans held for investment purposes during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The carrying amount, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of FHLB debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

+ Details

Name:	us-gaap_PledgedFinancialInstrumentsNotSeparatelyReportedLoansReceivablePledgedForFederalHomeLoanBankDebt
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Data Type:	xbrli:monetaryItemType
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- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_OneToFourSingleFamilyResidentialMember
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- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bku_CommercialFinanceSubsidiariesMember
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- Details

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- Details

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Loans and Allowance for Loan and Lease Losses (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Financing Receivable Investment Past Due [Line Items]
Purchases of loans			$ 913,840	$ 949,294
Unpaid principal balance of real estate loans pledged as security for FHLB advances	$ 10,200,000		10,200,000
Recorded investment of real estate loans pledged as security for FHLB advances	9,900,000		9,900,000
Unpaid principal balance of ACI loans	700,000		700,000		$ 1,100,000
Impaired Financing Receivable, Interest Income, Accrual Method		$ 2,900		8,300
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	2,101	1,415	4,951	3,691
1-4 single family residential
Financing Receivable Investment Past Due [Line Items]
Purchases of loans	309,562	$ 312,418	913,840	$ 949,294
Commercial Lending Subsidiaries
Financing Receivable Investment Past Due [Line Items]
Capital Leases, Net Investment in Direct Financing Leases	764,000		764,000		738,000
Residential and Other Consumer
Financing Receivable Investment Past Due [Line Items]
Mortgage Loans in Process of Foreclosure, Amount	1,000		1,000		11,000
Covered [Member] \| Residential and Other Consumer
Financing Receivable Investment Past Due [Line Items]
Other Real Estate, Foreclosed Assets, and Repossessed Assets	5,000		5,000		$ 3,000
Minimum \| Commercial
Financing Receivable Investment Past Due [Line Items]
Financing receivable credit quality indicator, the value at which relationships are reevaluated at least annually	1,000		1,000
Maximum [Member] \| Commercial
Financing Receivable Investment Past Due [Line Items]
Financing receivable credit quality indicator, the value at which relationships are reevaluated at least annually	3,000		3,000
US Government Agency Insured Loans [Member] \| 1-4 single family residential
Financing Receivable Investment Past Due [Line Items]
Purchases of loans	89,762		201,302
US Government Agency Insured Loans [Member] \| Residential and Other Consumer
Financing Receivable Investment Past Due [Line Items]
Mortgage Loans in Process of Foreclosure, Amount	$ 59,000		$ 59,000