Securities - Summary of Securities Available-for-Sale and Restricted Stock (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2025	Dec. 31, 2024
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost, Available-for-sale	$ 116,819	$ 134,736
Gross Unrealized Gains, Available-for-sale	219	43
Gross Unrealized Losses, Available-for-sale	(6,971)	(9,345)
Fair Value, Available-for-sale	110,067	125,434
Amortized Cost, Held to maturity	195,048	204,309
Gross Unrealized Losses, Held to maturity	(25,304)	(31,706)
Fair Value, Held to maturity	169,744	172,603
Amortized Cost	313,572	340,750
Gross Unrealized Gains	307	124
Gross Unrealized Losses	(32,275)	(41,051)
Fair Value	281,604	299,823
U.S. Treasury Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost, Available-for-sale	3,497	13,487
Gross Unrealized Gains, Available-for-sale		8
Gross Unrealized Losses, Available-for-sale	(1)	(81)
Fair Value, Available-for-sale	3,496	13,414
Amortized Cost, Held to maturity	7,877	7,854
Gross Unrealized Losses, Held to maturity	(430)	(621)
Fair Value, Held to maturity	7,447	7,233
U.S. Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost, Available-for-sale	6,000	6,000
Gross Unrealized Losses, Available-for-sale	(182)	(302)
Fair Value, Available-for-sale	5,818	5,698
Mortgage-Backed Securities of Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost, Available-for-sale	68,934	69,746
Gross Unrealized Gains, Available-for-sale	210	30
Gross Unrealized Losses, Available-for-sale	(5,497)	(7,078)
Fair Value, Available-for-sale	63,647	62,698
Amortized Cost, Held to maturity	184,669	193,937
Gross Unrealized Losses, Held to maturity	(24,704)	(30,862)
Fair Value, Held to maturity	159,965	163,075
Asset-Backed Securities of Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost, Available-for-sale	379	404
Gross Unrealized Losses, Available-for-sale	(10)	(6)
Fair Value, Available-for-sale	369	398
State and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost, Available-for-sale	15,011	15,051
Gross Unrealized Losses, Available-for-sale	(567)	(805)
Fair Value, Available-for-sale	14,444	14,246
Amortized Cost, Held to maturity	2,502	2,518
Gross Unrealized Losses, Held to maturity	(170)	(223)
Fair Value, Held to maturity	2,332	2,295
Corporate Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost, Available-for-sale	22,998	30,048
Gross Unrealized Gains, Available-for-sale	9	5
Gross Unrealized Losses, Available-for-sale	(714)	(1,073)
Fair Value, Available-for-sale	22,293	28,980
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost, Equity securities	185	185
Gross Unrealized Gains, Equity securities	88	81
Fair Value, Equity securities	273	266
Restricted Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized Cost	1,520	1,520
Fair Value	$ 1,520	$ 1,520

CSB Bancorp, Inc. 10-Q