Employee Benefit Plans - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 30, 2018 USD ($) shares	Dec. 31, 2021 USD ($)	Dec. 31, 2023 USD ($) yr	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Years of employment benefits are based upon			5 years
Bank-owned life insurance ("BOLI")			$ 268,362	$ 264,854
Bank-owned life insurance income		$ 6,000	10,126	7,393	$ 5,994
Defined contribution plan, cost			2,800
Defined contribution plan, employer discretionary contribution amount			245	204	213
Employee stock ownership plan, compensation expense			(4,095)	(4,850)	(4,052)
RIM Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			(13,550)	(12,610)
Defined contribution plan, cost			40	73	12
SERP compensation (benefit) expense			(32)	455	348
Defined benefit plan, net periodic benefit cost (credit)			966	1,205	1,405
RIM Plan | Acquired Roselle Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost (credit)			20	12	9
RIM Plan | Acquired Freehold Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost (credit)			2	8	1
RIM Plan | Acquired RSI Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost (credit)				38
Post-retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			$ (21,148)	(19,783)
Trend rate, pre-65 (as a percent)			0.0760
Trend rate, post-65 (as a percent)			0.0785
Trend rate, through 2033 (as a percent)			0.0450
Defined benefit plan, net periodic benefit cost (credit)			$ 1,185	1,257	1,695
Post-retirement Plan | Acquired RSI Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			(2,503)	(2,047)
Defined benefit plan, net periodic benefit cost (credit)			113	(244)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			197,691	181,620
Defined contribution plan, cost				2,400	2,100
Defined benefit plan, net periodic benefit cost (credit)			(13,659)	(11,966)	(9,471)
Pension Plan | Acquired RSI Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			0	1,004
Defined benefit plan, net periodic benefit cost (credit)			(182)	(107)
Other Pension, Postretirement and Supplemental Plans | Acquired Freehold Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost (credit)			(24)	9	1
Defined benefit plan, annual benefit payment amount			$ 12
Defined benefit plan, benefit payment installment period			120 months
Liability, defined benefit plan			$ 387	390
Other Pension, Postretirement and Supplemental Plans | Acquired RSI Plan
Defined Benefit Plan Disclosure [Line Items]
Liability, defined benefit plan			262	257
Defined benefit plan, expense			$ 11	7
Postemployment Retirement Benefits | Acquired Freehold Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, benefit payment installment period			120 months
Defined benefit plan, percent return on deferrals			10.00%
Liability, defined benefit plan			$ 66	399
Postemployment Retirement Benefits | Acquired RSI Plan
Defined Benefit Plan Disclosure [Line Items]
Liability, defined benefit plan			290	351
Defined benefit plan, expense			$ 11	8
Defined benefit plan, period directors elected not to receive director fees			5 years
Defined benefit plan, benefit payable accrual period			10 years
Defined benefit plan, payment commencement age | yr			65
Defined benefit plan, payment commencement period from plan implementation			5 years
Maximum
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match			4.50%
Maximum | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match			4.50%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match			3.00%
Minimum | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match			3.00%
Columbia Bank Employee Stock Ownership Plan
Defined Benefit Plan Disclosure [Line Items]
Proceeds from repayments of loans by employee stock ownership plans	$ 45,400
Loan term	20 years		20 years
Shares contributed to ESOP (in shares) | shares	4,542,855
Fixed interest rate	4.75%
Employee stock ownership plan, compensation expense			$ (4,100)	$ (4,900)	$ (4,100)