Business Combinations and Asset Acquisitions - Assets acquired and liabilities assumed (Details) - USD ($) $ in Thousands	Feb. 28, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Asset Acquisition [Line Items]
Goodwill		$ 1,029,234	$ 0
Umpqua Bank and Columbia Banking System Merger
Asset Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 2,339,278
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	274,587
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans held for Sale	2,358
Business Combination, Acquired Receivable, Fair Value	10,884,218
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Restricted Equity Securities	101,760
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	203,270
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	710,230
Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets	256,288
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Assets	571,773
Assets acquired	19,230,586	19,230,586		$ 0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits	15,193,474
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits - Securities Sold Under Agreements to Repurcahse	70,025
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits, Borrowings	2,294,360
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deposits - Junior and Other Subordinated Debentures	20,310
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Liabilities	342,373
Liabilities assumed	17,920,542	17,920,542		0
Net assets acquired	1,310,044	$ 1,310,044		$ 0
Goodwill	1,029,234
Umpqua Bank and Columbia Banking System Merger | Securities Investment
Asset Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities	$ 6,226,102