Financial Instruments with Off-Balance Sheet Credit Exposures - Schedule of Notional Amounts of Financial Instruments with Off-Balance Sheet Credit Risk (Detail) - USD ($) $ in Thousands |
Jun. 30, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Unadvanced portions of loans [Member] | ||
| Fair Value, off-Balance-Sheet Risks, Disclosure Information [Line Items] | ||
| Unadvanced portions of loans | $ 53,137 | $ 52,372 |
| Commitments to originate loans [Member] | ||
| Fair Value, off-Balance-Sheet Risks, Disclosure Information [Line Items] | ||
| Unadvanced portions of loans | 9,642 | 11,072 |
| Standby letters of credit [Member] | ||
| Fair Value, off-Balance-Sheet Risks, Disclosure Information [Line Items] | ||
| Unadvanced portions of loans | $ 538 | $ 262 |