Loans and Allowance for Credit Losses - Balance of Each Major Product Type (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Financing Receivable, Past Due [Line Items]
Subtotal	$ 3,889,549		$ 3,534,606
Net deferred loan fees	(2,290)		(1,920)
Loans held for investment	3,887,259		3,532,686
Allowance for credit losses	(42,061)	$ (40,167)	(37,791)	$ (37,583)	$ (35,406)	$ (34,431)
Loans held for investment, net of allowance for credit losses	3,845,198		3,494,895
Commercial
Financing Receivable, Past Due [Line Items]
Subtotal	3,144,303		2,857,173
Loans held for investment	3,141,402		2,854,531
Allowance for credit losses	(23,473)	(27,792)	(25,864)	(26,217)	(24,708)	(29,015)
Commercial land and development
Financing Receivable, Past Due [Line Items]
Subtotal	934		3,849
Loans held for investment	931		3,854
Allowance for credit losses	(30)	(33)	(78)	(89)	(72)	(178)
Commercial construction
Financing Receivable, Past Due [Line Items]
Subtotal	136,988		111,318
Loans held for investment	136,623		111,033
Allowance for credit losses	(4,355)	(2,575)	(2,268)	(1,756)	(1,097)	(718)
Residential construction
Financing Receivable, Past Due [Line Items]
Subtotal	5,976		4,561
Loans held for investment	5,913		4,560
Allowance for credit losses	(108)	(75)	(64)	(47)	(100)	(89)
Residential
Financing Receivable, Past Due [Line Items]
Subtotal	35,739		32,774
Loans held for investment	35,764		32,796
Allowance for credit losses	(351)	(334)	(270)	(284)	(195)	(151)
Farmland
Financing Receivable, Past Due [Line Items]
Subtotal	57,572		47,241
Loans held for investment	57,535		47,220
Allowance for credit losses	(425)	(723)	(607)	(581)	(402)	(399)
Secured
Financing Receivable, Past Due [Line Items]
Subtotal	191,170		170,548
Loans held for investment	192,046		171,336
Allowance for credit losses	(10,400)	(5,623)	(5,866)	(6,049)	(7,386)	(3,314)
Unsecured
Financing Receivable, Past Due [Line Items]
Subtotal	38,658		27,558
Loans held for investment	38,689		27,575
Allowance for credit losses	(438)	(417)	(278)	(251)	(214)	(189)
Consumer and other
Financing Receivable, Past Due [Line Items]
Subtotal	278,209		279,584
Loans held for investment	278,356		279,781
Allowance for credit losses	$ (2,481)	$ (2,595)	$ (2,496)	$ (2,309)	$ (1,232)	$ (378)

FIVE STAR BANCORP 10-Q