Commitments and Contingencies (Narrative) (Details) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
	Nov. 15, 2022 USD ($) branches shares	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Financial guarantees in connection with standby letters of credit		$ 0.0	$ 0.0	$ 0.0	$ 0.0
Standby letters of credit expiring within one year		115.6		115.6
Standby letters of credit expiring thereafter		$ 9.7		$ 9.7
Expected
Concentration Risk [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Share Exchange Ratio | shares	0.5958
Termination Fee	$ 145.0
Expected | Umpqua Bank and Columbia Banking System Merger
Concentration Risk [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired	62.00%
Number of Stores to be Divested | branches	10
Expected | Umpqua Bank and Columbia Banking System Merger | Columbia Banking System, Inc.
Concentration Risk [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired	38.00%
Product Concentration Risk | Revenue Benchmark | Real Estate Loans As Part Of Loan Portfolio
Concentration Risk [Line Items]
Concentration risk (as a percent)				78.00%		76.00%