v3.26.1
Fair Value Measurements (Details) - EBP 002 - USD ($)
$ in Thousands
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value $ 42,861 $ 35,892
Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 36,522 29,405
Common Stock of Northfield Bancorp, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 3,223 3,520
Self-directed brokerage account    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 1,803 1,576
Fair Value, Inputs, Level 1, Level 2, and Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 41,548 34,501
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 36,522 29,405
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Common Stock of Northfield Bancorp, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 3,223 3,520
Fair Value, Inputs, Level 1, Level 2, and Level 3 | Self-directed brokerage account    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 1,803 1,576
Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 41,548 34,501
Level 1 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 36,522 29,405
Level 1 | Common Stock of Northfield Bancorp, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 3,223 3,520
Level 1 | Self-directed brokerage account    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 1,803 1,576
Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 0
Level 2 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 0 0
Level 2 | Common Stock of Northfield Bancorp, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 0 0
Level 2 | Self-directed brokerage account    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 0 0
Level 3    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 0
Level 3 | Mutual funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 0 0
Level 3 | Common Stock of Northfield Bancorp, Inc.    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 0 0
Level 3 | Self-directed brokerage account    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value 0 0
Investments measured at Net Asset Value    
EBP, Investment, Fair Value and NAV [Line Items]    
Total investments at fair value $ 1,313 $ 1,391