PARENT COMPANY ONLY FINANCIAL INFORMATION - Parent Only Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Condensed Balance Sheet Statements, Captions [Line Items]
Other assets	$ 2,411	$ 904
Total assets	312,114	280,939
Liabilities:
Other liabilities	6,981	2,908
Total liabilities	279,363	257,081
Stockholders' equity:
Total stockholders' equity	32,751	23,858	$ 22,649
Total liabilities and stockholders' equity	312,114	280,939
Seneca Financial Corp (Parent Company)
Condensed Balance Sheet Statements, Captions [Line Items]
Cash in bank subsidiary	3,268	79
Investments in subsidiaries, at underlying equity	27,681	23,068
Loan receivable - ESOP	1,420	666
Other assets	754	45
Total assets	33,123	23,858
Liabilities:
Other liabilities	372
Total liabilities	372
Stockholders' equity:
Total stockholders' equity	32,751	23,858
Total liabilities and stockholders' equity	$ 33,123	$ 23,858