XML 66 R23.htm IDEA: XBRL DOCUMENT
v3.25.2

Investment Securities (Tables) | 6 Months Ended
--- | ---
Jun. 30, 2025
Investments, Debt and Equity Securities [Abstract] |
Schedule of Available-for-sale Securities Reconciliation | Investment securities include investment securities available for sale and marketable equity securities. The investment securities portfolio consisted of the following at the dates indicated (in thousands):
| June 30, 2025
| Amortized Cost |  | Gross Unrealized |  | Carrying Value
|  | Gains |  | Losses |
Investment securities available for sale: |  |  |  |  |  |  |
U.S. Treasury securities | $ | 149,875 |  |  | $ | 998 |  |  | $ | (8,304) |  |  | $ | 142,569 |
U.S. Government agency and sponsored enterprise residential MBS | 2,721,476 |  |  | 10,330 |  |  | (19,268) |  |  | 2,712,538 |
U.S. Government agency and sponsored enterprise commercial MBS | 548,402 |  |  | 450 |  |  | (48,527) |  |  | 500,325 |
Private label residential MBS and CMOs | 2,586,509 |  |  | 1,502 |  |  | (226,507) |  |  | 2,361,504 |
Private label commercial MBS | 2,119,814 |  |  | 2,902 |  |  | (27,677) |  |  | 2,095,039 |
Single family real estate-backed securities | 207,306 |  |  | 240 |  |  | (4,193) |  |  | 203,353 |
Collateralized loan obligations | 1,119,184 |  |  | 690 |  |  | (1,043) |  |  | 1,118,831 |
Non-mortgage asset-backed securities | 91,483 |  |  | 6 |  |  | (1,699) |  |  | 89,790 |
State and municipal obligations | 111,897 |  |  | 51 |  |  | (8,074) |  |  | 103,874 |
SBA securities | 66,443 |  |  | 27 |  |  | (1,901) |  |  | 64,569 |
| $ | 9,722,389 |  |  | $ | 17,196 |  |  | $ | (347,193) |  |  | $ | 9,392,392 |
Marketable equity securities |  |  |  |  |  |  | 8,679 |
|  |  |  |  |  |  | $ | 9,401,071 |
| December 31, 2024
| Amortized Cost |  | Gross Unrealized |  | Carrying Value
|  | Gains |  | Losses |
Investment securities available for sale: |  |  |  |  |  |  |
U.S. Treasury securities | $ | 214,796 |  |  | $ | 165 |  |  | $ | (12,009) |  |  | $ | 202,952 |
U.S. Government agency and sponsored enterprise residential MBS | 2,672,554 |  |  | 3,607 |  |  | (26,471) |  |  | 2,649,690 |
U.S. Government agency and sponsored enterprise commercial MBS | 557,489 |  |  | 156 |  |  | (61,892) |  |  | 495,753 |
Private label residential MBS and CMOs | 2,491,033 |  |  | 506 |  |  | (253,493) |  |  | 2,238,046 |
Private label commercial MBS | 1,822,881 |  |  | 1,836 |  |  | (40,688) |  |  | 1,784,029 |
Single family real estate-backed securities | 335,047 |  |  | 108 |  |  | (8,074) |  |  | 327,081 |
Collateralized loan obligations | 1,131,088 |  |  | 1,804 |  |  | (193) |  |  | 1,132,699 |
Non-mortgage asset-backed securities | 96,865 |  |  | 144 |  |  | (2,555) |  |  | 94,454 |
State and municipal obligations | 110,388 |  |  | 13 |  |  | (6,391) |  |  | 104,010 |
SBA securities | 74,900 |  |  | 37 |  |  | (2,235) |  |  | 72,702 |
| $ | 9,507,041 |  |  | $ | 8,376 |  |  | $ | (414,001) |  |  | $ | 9,101,416 |
Marketable equity securities |  |  |  |  |  |  | 28,828 |
|  |  |  |  |  |  | $ | 9,130,244 |
Investments Classified by Contractual Maturity Date | At June 30, 2025, contractual maturities of investment securities available for sale, adjusted for anticipated prepayments when applicable, were as follows (in thousands):
| Amortized Cost |  | Fair Value
Due in one year or less | $ | 801,840 |  |  | $ | 781,538 |
Due after one year through five years | 5,300,383 |  |  | 5,211,984 |
Due after five years through ten years | 2,429,925 |  |  | 2,304,295 |
Due after ten years | 1,190,241 |  |  | 1,094,575 |
| $ | 9,722,389 |  |  | $ | 9,392,392 |
Gain on Investment Securities, net | The following table provides information about gains (losses) on investment securities for the periods indicated (in thousands):
| Three Months Ended June 30, |  | Six Months Ended June 30,
| 2025 |  | 2024 |  | 2025 |  | 2024 |  |
Gross realized gains on investment securities AFS | $ | 731 |  |  | $ | 398 |  |  | $ | 1,593 |  |  | $ | 425 |  |  |
Gross realized losses on investment securities AFS | (118) |  |  | (48) |  |  | (155) |  |  | (103) |  |  |
Net realized gain | 613 |  |  | 350 |  |  | 1,438 |  |  | 322 |  |  |
Net gain (loss) on marketable equity securities recognized in earnings | (266) |  |  | 71 |  |  | (147) |  |  | 874 |  |  |
Gain on investment securities, net | $ | 347 |  |  | $ | 421 |  |  | $ | 1,291 |  |  | $ | 1,196 |  |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value | The following tables present the aggregate fair value and the aggregate amount by which amortized cost exceeded fair value for investment securities available for sale in unrealized loss positions aggregated by investment category and length of time that individual securities had been in continuous unrealized loss positions at the dates indicated (in thousands):
| June 30, 2025
| Less than 12 Months |  | 12 Months or Greater |  | Total
| Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses
U.S. Treasury securities | $ | 53,724 |  |  | $ | (1,442) |  |  | $ | 42,776 |  |  | $ | (6,862) |  |  | $ | 96,500 |  |  | $ | (8,304) |
U.S. Government agency and sponsored enterprise residential MBS | 334,189 |  |  | (2,077) |  |  | 711,375 |  |  | (17,191) |  |  | 1,045,564 |  |  | (19,268) |
U.S. Government agency and sponsored enterprise commercial MBS | 37,967 |  |  | (376) |  |  | 401,394 |  |  | (48,151) |  |  | 439,361 |  |  | (48,527) |
Private label residential MBS and CMOs | 201,978 |  |  | (1,503) |  |  | 1,967,841 |  |  | (225,004) |  |  | 2,169,819 |  |  | (226,507) |
Private label commercial MBS | 440,202 |  |  | (1,056) |  |  | 633,038 |  |  | (26,621) |  |  | 1,073,240 |  |  | (27,677) |
Single family real estate-backed securities | — |  |  | — |  |  | 156,151 |  |  | (4,193) |  |  | 156,151 |  |  | (4,193) |
Collateralized loan obligations | 573,567 |  |  | (1,043) |  |  | — |  |  | — |  |  | 573,567 |  |  | (1,043) |
Non-mortgage asset-backed securities | — |  |  | — |  |  | 68,714 |  |  | (1,699) |  |  | 68,714 |  |  | (1,699) |
State and municipal obligations | 15,813 |  |  | (72) |  |  | 51,218 |  |  | (8,002) |  |  | 67,031 |  |  | (8,074) |
SBA securities | — |  |  | — |  |  | 60,862 |  |  | (1,901) |  |  | 60,862 |  |  | (1,901) |
| $ | 1,657,440 |  |  | $ | (7,569) |  |  | $ | 4,093,369 |  |  | $ | (339,624) |  |  | $ | 5,750,809 |  |  | $ | (347,193) |
| December 31, 2024
| Less than 12 Months |  | 12 Months or Greater |  | Total
| Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses |  | Fair Value |  | Unrealized Losses
U.S. Treasury securities | $ | 126,710 |  |  | $ | (3,195) |  |  | $ | 40,791 |  |  | $ | (8,814) |  |  | $ | 167,501 |  |  | $ | (12,009) |
U.S. Government agency and sponsored enterprise residential MBS | 895,759 |  |  | (5,474) |  |  | 936,106 |  |  | (20,997) |  |  | 1,831,865 |  |  | (26,471) |
U.S. Government agency and sponsored enterprise commercial MBS | 55,431 |  |  | (1,545) |  |  | 394,735 |  |  | (60,347) |  |  | 450,166 |  |  | (61,892) |
Private label residential MBS and CMOs | 147,700 |  |  | (954) |  |  | 2,040,335 |  |  | (252,539) |  |  | 2,188,035 |  |  | (253,493) |
Private label commercial MBS | 44,000 |  |  | (302) |  |  | 1,199,150 |  |  | (40,386) |  |  | 1,243,150 |  |  | (40,688) |
Single family real estate-backed securities | — |  |  | — |  |  | 301,973 |  |  | (8,074) |  |  | 301,973 |  |  | (8,074) |
Collateralized loan obligations | 336,924 |  |  | (189) |  |  | 7,726 |  |  | (4) |  |  | 344,650 |  |  | (193) |
Non-mortgage asset-backed securities | — |  |  | — |  |  | 71,789 |  |  | (2,555) |  |  | 71,789 |  |  | (2,555) |
State and municipal obligations | 15,765 |  |  | (148) |  |  | 54,820 |  |  | (6,243) |  |  | 70,585 |  |  | (6,391) |
SBA securities | — |  |  | — |  |  | 67,880 |  |  | (2,235) |  |  | 67,880 |  |  | (2,235) |
| $ | 1,622,289 |  |  | $ | (11,807) |  |  | $ | 5,115,305 |  |  | $ | (402,194) |  |  | $ | 6,737,594 |  |  | $ | (414,001) |

X
- Definition [Table Text Block] for Gain on Investment Securities, net [Table] + References No definition available. + Details
Name: | bku_GainonInvestmentSecuritiesnetTableTextBlock
Namespace Prefix: | bku_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 55 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479081/326-30-55-8 Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-6 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479106/326-30-50-4 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments. + References No definition available. + Details
Name: | us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value. + References No definition available. + Details
Name: | us-gaap_ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration