Significant Accounting Policies - Administrative Expenses (Details) - Community Financial System, Inc. 401(k) Employee Stock Ownership Plan - USD ($) |
12 Months Ended | |
|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
|
| Significant Accounting Policies | ||
| Amount paid for record keeping, trustee, and other services | $ 1,532,000 | $ 1,585,000 |
| Trustee | ||
| Significant Accounting Policies | ||
| Amount paid for record keeping, trustee, and other services | $ 1,550,000 | $ 1,453,000 |