Summary of Significant Accounting Policies (Details) - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2022	Dec. 31, 2020	Nov. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Assets		$ 10,645,568,000	$ 10,408,169,000
Loan threshold for individual evaluation for impairment		$ 500,000
Operating Lease, Liability, Statement of Financial Position [Extensible List]		Other Liabilities	Other Liabilities
Years of employment benefits are based upon		5 years
Unrecognized tax benefits		$ 0	$ 0
Income tax penalties and interest expense		0	0	$ 0
Allowance for credit losses on loans		55,096,000	52,803,000	62,689,000		$ 74,676,000
Allowance for credit losses on debt securities available for sale		0	0	0
Off-balance sheet, credit loss, liability		5,484,000	6,970,000	524,000
Stockholders' equity		1,040,335,000	1,053,595,000	1,079,081,000		1,011,287,000
Impact of adopting ASU 2016-13 (CECL) effective January 1, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Allowance for credit losses on loans			0	(16,443,000)		0
Allowance for credit losses on debt securities available for sale				490,000
Stockholders' equity				6,212,000
Retained Earnings
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Stockholders' equity		$ 893,604,000	$ 857,518,000	765,133,000		$ 673,084,000
Retained Earnings | Impact of adopting ASU 2016-13 (CECL) effective January 1, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Stockholders' equity				6,212,000
Accounting Standards Update 2016-13 | Impact of adopting ASU 2016-13 (CECL) effective January 1, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Allowance for credit losses on loans					$ 12,100,000
Allowance for credit losses on debt securities available for sale					353,000
Off-balance sheet, credit loss, liability				$ 7,674,000	5,500,000
Accounting Standards Update 2016-13 | Retained Earnings | Impact of adopting ASU 2016-13 (CECL) effective January 1, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Stockholders' equity					$ (6,200,000)
Columbia Bank Employee Stock Ownership Plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Loan term	20 years	20 years
Buildings
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		40 years
Minimum
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Defined contribution plan, employer matching contribution, percent of match		3.00%
Minimum | Land and building improvements
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		10 years
Minimum | Furniture and equipment
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		3 years
Maximum
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Defined contribution plan, employer matching contribution, percent of match		4.50%
Maximum | Land and building improvements
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		20 years
Maximum | Furniture and equipment
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Property, plant and equipment, useful life		10 years
Variable Interest Entity, Not Primary Beneficiary
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Assets							$ 7,000,000
Stewardship Statutory Trust I
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Ownership percentage by parent							100.00%