Employee Benefit Plans - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Years of employment benefits are based upon			5 years
Bank-owned life insurance ("BOLI")			$ 247,474,000	$ 232,824,000
Bank-owned life insurance income		$ 5,800,000	5,994,000	6,620,000	$ 5,846,000
Employee stock ownership plan, compensation expense			4,052,000	$ 3,161,000	$ 3,566,000
Options exercised in period, intrinsic value			$ 59,991
Exercises in period (in shares)			28,522	0	0
RIM Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			$ (15,650,000)	$ (16,530,000)
Defined contribution plan, cost			12,000	4,000	$ 11,000
Employee stock ownership plan, compensation expense			348,000	215,000	267,000
Defined benefit plan, net periodic benefit cost (credit)			1,405,000	1,069,000	920,000
RIM Plan | Roselle Entities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost (credit)			9,000	11,000
RIM Plan | Freehold Entities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost (credit)			1,000
Post-retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			(26,335,000)	(30,621,000)
Defined benefit plan, net periodic benefit cost (credit)			1,695,000	1,386,000	1,312,000
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, funded (unfunded) status of plan			181,716,000	99,467,000
Defined contribution plan, cost			1,900,000	1,700,000	1,400,000
Defined benefit plan, net periodic benefit cost (credit)			(9,471,000)	(2,880,000)	(2,925,000)
Other Pension, Postretirement and Supplemental Plans | Freehold Entities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, net periodic benefit cost (credit)			$ 1,000
Defined benefit plan, benefit payment installment period			120 months
Defined benefit plan, annual benefit payment amount			$ 12,000
Postemployment Retirement Benefits | Freehold Entities
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			$ 765,000
Defined benefit plan, expense			$ 0
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	$ 45,400,000
Loan term	20 years		20 years
Shares contributed to ESOP (in shares)	4,542,855
Fixed interest rate	4.75%
Employee stock ownership plan, compensation expense			$ 4,100,000	$ 3,200,000	$ 3,600,000