Business Combinations and Asset Acquisitions - Narrative (Details) $ in Thousands		3 Months Ended	9 Months Ended
	Feb. 28, 2023 USD ($) shares	Jun. 30, 2023 USD ($)	Sep. 30, 2023 USD ($) shares	Feb. 24, 2023 branch	Jan. 20, 2023 branch	Dec. 31, 2022 shares	[1]
Asset Acquisition [Line Items]
Common stock, shares outstanding			208,575,479			129,320,962
Goodwill, Period Decrease | $		$ 908
Disposal Group, Disposed of by Sale, Not Discontinued Operations | First Norther Bank of Dixon
Asset Acquisition [Line Items]
Branch locations disposed of by sale - number | branch					3
Disposal Group, Disposed of by Sale, Not Discontinued Operations | 1st Security Bank
Asset Acquisition [Line Items]
Branch locations disposed of by sale - number | branch				7
Umpqua Bank and Columbia Banking System Merger
Asset Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Share Exchange Ratio	0.5958
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	208,241,000
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Business Combination, Acquired Receivable, Fair Value | $	$ 10,884,218
Financing Receivable, Purchased with Credit Deterioration, Amount at Purchase Price | $	$ 402,819
Business Combination, Acquisition Related Costs - Combined for proforma | $			$ 192,500
Umpqua Bank and Columbia Banking System Merger | Columbia Banking System, Inc.
Asset Acquisition [Line Items]
Common stock, shares outstanding	208,200,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	78,863,000
Business Acquisition, Percentage of Voting Interests Acquired	37.90%
Umpqua Bank and Columbia Banking System Merger | UHC
Asset Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	129,378,000
Business Acquisition, Percentage of Voting Interests Acquired	62.10%

[1] Periods prior to February 28, 2023 have been restated as a result of the adjustment to common shares outstanding based on the exchange ratio from the Merger of 0.5958.