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Investments (Tables) | 3 Months Ended
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Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract] |
Schedule of amortized cost, estimated fair value, and allowance for credit losses of available-for-sale and held-to-maturity investment securities | The amortized cost, estimated fair value, and allowance for credit losses of available-for-sale and held-to-maturity investment securities are as follows: Amortized Cost and Estimated Fair Value (dollars in thousands, unaudited)
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | March 31, 2024
​ |  | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses | ​ | Allowance for Credit Losses |  | Estimated Fair Value
Available-for-sale | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government agencies | ​ | $ | 65,579 | ​ | $ | 7 | ​ | $ | (149) | ​ | $ | — | ​ | $ | 65,437
Mortgage-backed securities | ​ | ​ | 14,181 | ​ | ​ | 18 | ​ | ​ | (751) | ​ | ​ | — | ​ | ​ | 13,448
State and political subdivisions | ​ | ​ | 51,060 | ​ | ​ | 81 | ​ | ​ | (6,466) | ​ | ​ | — | ​ | ​ | 44,675
Corporate bonds | ​ | ​ | 65,303 | ​ | ​ | — | ​ | ​ | (10,644) | ​ | ​ | — | ​ | ​ | 54,659
Collateralized loan obligations | ​ | ​ | 563,099 | ​ | ​ | 1,478 | ​ | ​ | (1,007) | ​ | ​ | — | ​ | ​ | 563,570
Total available-for-sale securities | ​ | $ | 759,222 | ​ | $ | 1,584 | ​ | $ | (19,017) | ​ | $ | — | ​ | $ | 741,789
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized Cost |  | Gross Unrecognized Gains |  | Gross Unrecognized Losses | ​ | Estimated Fair Value |  | Allowance for Credit Losses
Held-to-maturity | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government agencies | ​ | $ | 5,033 | ​ | $ | — | ​ | $ | (652) | ​ | $ | 4,381 | ​ | $ | —
Mortgage-backed securities | ​ | ​ | 139,225 | ​ | ​ | — | ​ | ​ | (12,585) | ​ | ​ | 126,640 | ​ | ​ | —
State and political subdivisions | ​ | ​ | 172,164 | ​ | ​ | 2,971 | ​ | ​ | — | ​ | ​ | 175,135 | ​ | ​ | (16)
Total held-to-maturity securities | ​ | $ | 316,422 | ​ | $ | 2,971 | ​ | $ | (13,237) | ​ | $ | 306,156 | ​ | $ | (16)
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2023
​ |  | Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses | ​ | Allowance for Credit Losses |  | Estimated Fair Value
Available-for-sale | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government agencies | ​ | $ | 102,823 | ​ | $ | 23 | ​ | $ | (97) | ​ | $ | — | ​ | $ | 102,749
Mortgage-backed securities | ​ | ​ | 100,745 | ​ | ​ | 21 | ​ | ​ | (1,222) | ​ | ​ | — | ​ | ​ | 99,544
State and political subdivisions | ​ | ​ | 200,057 | ​ | ​ | 572 | ​ | ​ | (6,423) | ​ | ​ | — | ​ | ​ | 194,206
Corporate bonds | ​ | ​ | 65,273 | ​ | ​ | — | ​ | ​ | (13,233) | ​ | ​ | — | ​ | ​ | 52,040
Collateralized loan obligations | ​ | ​ | 573,027 | ​ | ​ | 1,113 | ​ | ​ | (3,478) | ​ | ​ | — | ​ | ​ | 570,662
Total available-for-sale securities | ​ | $ | 1,041,925 | ​ | $ | 1,729 | ​ | $ | (24,453) | ​ | $ | — | ​ | $ | 1,019,201
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized Cost | ​ | Gross Unrecognized Gains | ​ | Gross Unrecognized Losses | ​ | Estimated Fair Value | ​ | Allowance for Credit Losses
Held-to-maturity | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government agencies | ​ | $ | 5,522 | ​ | $ | — | ​ | $ | (617) | ​ | $ | 4,905 | ​ | $ | —
Mortgage-backed securities | ​ | ​ | 142,295 | ​ | ​ | — | ​ | ​ | (10,441) | ​ | ​ | 131,854 | ​ | ​ | —
State and political subdivisions | ​ | ​ | 172,256 | ​ | ​ | 5,909 | ​ | ​ | — | ​ | ​ | 178,165 | ​ | ​ | (16)
Total held-to-maturity securities | ​ | $ | 320,073 | ​ | $ | 5,909 | ​ | $ | (11,058) | ​ | $ | 314,924 | ​ | $ | (16)
Schedule of amortized cost of held-to-maturity municipal bonds aggregated by NRSRO credit rating | Held-To-Maturity by Credit Rating (dollars in thousands, unaudited)
​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | Held-To-Maturity
​ | ​ | March 31, 2024 | ​ | December 31, 2023
State and political subdivisions | ​ | ​ | ​ | ​ | ​ | ​
AAA/Aaa | ​ | $ | 57,781 | ​ | $ | 57,792
AA/Aa | ​ | ​ | 112,901 | ​ | ​ | 112,978
A/A2 | ​ | ​ | 540 | ​ | ​ | 542
Not rated | ​ | ​ | 942 | ​ | ​ | 944
Total | ​ | $ | 172,164 | ​ | $ | 172,256
Information Pertaining to Investment Securities Aggregated by Investment Category and Length of Time that Individual Securities in a Continuous Loss Position | The following table summarizes available-for-sale debt securities that were in an unrealized loss position for which an ACL has not been recorded, based on the length of time the individual securities have been in an unrealized loss position, including the number of available-for-sale debt securities in an unrealized loss position, as of the dates indicated below. Investment Portfolio - Unrealized Losses (dollars in thousands, unaudited) ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | March 31, 2024
​ | ​ | ​ | Less than twelve months | ​ | Twelve months or more | ​ | Total
​ | Number of Securities |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses |  | Fair Value
Available-for-sale | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government agencies | 14 | ​ | $ | (62) | ​ | $ | 25,523 | ​ | $ | (87) | ​ | $ | 27,913 | ​ | $ | (149) | ​ | $ | 53,436
Mortgage-backed securities | 39 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | (751) | ​ | ​ | 9,578 | ​ | ​ | (751) | ​ | ​ | 9,578
State and political subdivisions | 48 | ​ | ​ | (1) | ​ | ​ | 201 | ​ | ​ | (6,465) | ​ | ​ | 35,646 | ​ | ​ | (6,466) | ​ | ​ | 35,847
Corporate bonds | 51 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | (10,644) | ​ | ​ | 54,659 | ​ | ​ | (10,644) | ​ | ​ | 54,659
Collateralized loan obligations | 29 | ​ | ​ | (378) | ​ | ​ | 133,658 | ​ | ​ | (629) | ​ | ​ | 126,235 | ​ | ​ | (1,007) | ​ | ​ | 259,893
Total available-for-sale | 181 | ​ | $ | (441) | ​ | $ | 159,382 | ​ | $ | (18,576) | ​ | $ | 254,031 | ​ | $ | (19,017) | ​ | $ | 413,413
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | December 31, 2023
​ | ​ | ​ | Less than twelve months | ​ | Twelve months or more | ​ | Total
​ | Number of Securities |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses |  | Fair Value |  | Gross Unrealized Losses |  | Fair Value
Available-for-sale | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
U.S. government agencies | 14 | ​ | $ | (97) | ​ | $ | 46,823 | ​ | $ | — | ​ | $ | 3,929 | ​ | $ | (97) | ​ | $ | 50,752
Mortgage-backed securities | 321 | ​ | ​ | — | ​ | ​ | 20 | ​ | ​ | (1,222) | ​ | ​ | 94,505 | ​ | ​ | (1,222) | ​ | ​ | 94,525
State and political subdivisions | 201 | ​ | ​ | (33) | ​ | ​ | 6,950 | ​ | ​ | (6,390) | ​ | ​ | 125,283 | ​ | ​ | (6,423) | ​ | ​ | 132,233
Corporate bonds | 51 | ​ | ​ | (118) | ​ | ​ | 2,316 | ​ | ​ | (13,115) | ​ | ​ | 49,724 | ​ | ​ | (13,233) | ​ | ​ | 52,040
Collateralized loan obligations | 47 | ​ | ​ | — | ​ | ​ | — | ​ | ​ | (3,478) | ​ | ​ | 393,258 | ​ | ​ | (3,478) | ​ | ​ | 393,258
Total available-for-sale | 634 | ​ | $ | (248) | ​ | $ | 56,109 | ​ | $ | (24,205) | ​ | $ | 666,699 | ​ | $ | (24,453) | ​ | $ | 722,808
Schedule of gross realized gains and losses as well as gross proceeds from the sales of securities | The table below summarizes the Company’s gross realized gains and losses as well as gross proceeds from the sales of securities, for the periods indicated: Investment Portfolio - Realized Gains/(Losses) (dollars in thousands, unaudited) ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three months ended March 31,
​ |  | 2024 |  | 2023
Proceeds from sales, calls and maturities of securities available for sale | ​ | $ | 266,900 | ​ | $ | 36,213
Gross gains on sales, calls and maturities of securities available for sale | ​ | ​ | 54 | ​ | ​ | 45
Gross losses on sales, calls and maturities of securities available for sale | ​ | ​ | (17,371) | ​ | ​ | —
Net (loss) gain on sale of securities available for sale | ​ | $ | (17,317) | ​ | $ | 45
Schedule of amortized cost and estimated fair value of investment securities available-for-sale and held-to-maturity grouped by the remaining time to contractual maturity dates | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | March 31, 2024
​ | ​ | Available-for-Sale | ​ | Held-to-Maturity
​ |  | Amortized Cost |  | Fair Value |  | Amortized Cost |  | Fair Value
Maturing within one year | ​ | $ | 2,200 | ​ | $ | 2,202 | ​ | $ | 145 | ​ | $ | 145
Maturing after one year through five years | ​ | ​ | 22,034 | ​ | ​ | 21,914 | ​ | ​ | 2,401 | ​ | ​ | 2,358
Maturing after five years through ten years | ​ | ​ | 102,687 | ​ | ​ | 92,029 | ​ | ​ | 19,362 | ​ | ​ | 17,771
Maturing after ten years | ​ | ​ | 55,021 | ​ | ​ | 48,626 | ​ | ​ | 155,289 | ​ | ​ | 159,242
Securities not due at a single maturity date: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Mortgage-backed securities | ​ | ​ | 14,181 | ​ | ​ | 13,448 | ​ | ​ | 139,225 | ​ | ​ | 126,640
Collateralized loan obligations | ​ | ​ | 563,099 | ​ | ​ | 563,570 | ​ | ​ | — | ​ | ​ | —
Total | ​ | $ | 759,222 | ​ | $ | 741,789 | ​ | $ | 316,422 | ​ | $ | 306,156
​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | December 31, 2023
​ | ​ | Available-for-Sale | ​ | Held-to-Maturity
​ |  | Amortized Cost |  | Fair Value |  | Amortized Cost |  | Fair Value
Maturing within one year | ​ | $ | 583 | ​ | $ | 582 |  | $ | 145 | ​ | $ | 145
Maturing after one year through five years | ​ | ​ | 40,187 | ​ | ​ | 39,916 | ​ | ​ | 2,413 | ​ | ​ | 2,384
Maturing after five years through ten years | ​ | ​ | 156,541 | ​ | ​ | 143,516 | ​ | ​ | 19,895 | ​ | ​ | 18,350
Maturing after ten years | ​ | ​ | 170,842 | ​ | ​ | 164,981 | ​ | ​ | 155,325 | ​ | ​ | 162,191
Securities not due at a single maturity date: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Mortgage-backed securities | ​ | ​ | 100,745 | ​ | ​ | 99,544 | ​ | ​ | 142,295 | ​ | ​ | 131,854
Collateralized loan obligations | ​ | ​ | 573,027 | ​ | ​ | 570,662 | ​ | ​ | — | ​ | ​ | —
Total | ​ | $ | 1,041,925 | ​ | $ | 1,019,201 | ​ | $ | 320,073 | ​ | $ | 314,924
Summary of Amortized Cost and Fair Values of General Obligation and Revenue Bonds | The following table summarizes the amortized cost and fair values of general obligation and revenue bonds in the Company’s investment securities portfolio at the indicated dates, identifying the state in which the issuing municipality or agency operates for our largest geographic concentrations: Revenue and General Obligation Bonds by Location (dollars in thousands, unaudited) ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | March 31, 2024 | ​ | December 31, 2023
​ | ​ | Amortized | ​ | Fair Market | ​ | Amortized | ​ | Fair Market
General obligation bonds |  | Cost |  | Value |  | Cost |  | Value
State of issuance | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Texas | ​ | $ | 83,196 | ​ | $ | 82,208 | ​ | $ | 146,215 | ​ | $ | 146,589
California | ​ | ​ | 51,523 | ​ | ​ | 49,174 | ​ | ​ | 63,316 | ​ | ​ | 61,048
Other (20 & 26 states, respectively) | ​ | ​ | 63,033 | ​ | ​ | 63,238 | ​ | ​ | 115,148 | ​ | ​ | 117,006
Total general obligation bonds | ​ | ​ | 197,752 | ​ | ​ | 194,620 | ​ | ​ | 324,679 | ​ | ​ | 324,643
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Revenue bonds | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
State of issuance | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Texas | ​ | ​ | 5,438 | ​ | ​ | 5,393 | ​ | ​ | 8,850 | ​ | ​ | 8,899
California | ​ | ​ | 3,571 | ​ | ​ | 3,496 | ​ | ​ | 3,794 | ​ | ​ | 3,735
Other (20 & 15 states, respectively) | ​ | ​ | 16,463 | ​ | ​ | 16,301 | ​ | ​ | 34,990 | ​ | ​ | 35,094
Total revenue bonds | ​ | ​ | 25,472 | ​ | ​ | 25,190 | ​ | ​ | 47,634 | ​ | ​ | 47,728
Total obligations of states and political subdivisions | ​ | $ | 223,224 | ​ | $ | 219,810 | ​ | $ | 372,313 | ​ | $ | 372,371
​ The revenue bonds in the Company’s investment securities portfolios were issued by government municipalities and agencies to fund public services such as utilities (water, sewer, and power), educational facilities, and general public and economic improvements. The primary sources of revenue for these bonds are delineated in the table below, which shows the amortized cost and fair market values for the largest revenue concentrations as of the indicated dates. Revenue Bonds by Type (dollars in thousands, unaudited) ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | March 31, 2024 | ​ | December 31, 2023
​ | ​ | Amortized | ​ | Fair Market | ​ | Amortized | ​ | Fair Market
Revenue bonds |  | Cost |  | Value |  | Cost |  | Value
Revenue source: | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
Water | ​ | $ | 9,211 | ​ | $ | 9,064 | ​ | $ | 19,113 | ​ | $ | 19,158
Lease | ​ | ​ | 3,932 | ​ | ​ | 4,210 | ​ | ​ | 6,323 | ​ | ​ | 6,380
Sewer | ​ | ​ | 3,607 | ​ | ​ | 3,760 | ​ | ​ | 6,070 | ​ | ​ | 6,312
Sales tax revenue | ​ | ​ | 1,690 | ​ | ​ | 1,630 | ​ | ​ | 4,349 | ​ | ​ | 4,010
Local or GTD housing | ​ | ​ | 1,032 | ​ | ​ | 852 | ​ | ​ | — | ​ | ​ | —
Other (9 and 10 sources, respectively) | ​ | ​ | 6,000 | ​ | ​ | 5,674 | ​ | ​ | 11,779 | ​ | ​ | 11,868
Total revenue bonds | ​ | $ | 25,472 | ​ | $ | 25,190 | ​ | $ | 47,634 | ​ | $ | 47,728

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- 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 and held-to-maturity), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References No definition available. + Details
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