Parent-only Financial Information - Condensed Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Interest expense on subordinated debt	$ 3,320	$ 1,797	$ 0
Income tax (benefit) expense	14,091	23,740	26,473
Net income	37,669	61,119	70,654
Other comprehensive income (loss), net of tax	15,889	(50,394)	(11,097)
Comprehensive income	53,558	10,725	59,557
Parent Company
Interest on ESOP loan	1,336	627	677
Interest income on deposits in other financial institutions	489	4	18
Undistributed earnings of Northfield Bank	39,662	62,964	70,956
Total income	41,487	63,595	71,651
Interest expense on subordinated debt	3,320	1,797	0
Other expenses	900	1,020	831
Income tax (benefit) expense	(402)	(341)	166
Total expenses	3,818	2,476	997
Net income	37,669	61,119	70,654
Other comprehensive income (loss), net of tax	15,889	(50,394)	(11,097)
Comprehensive income	$ 53,558	$ 10,725	$ 59,557