Consolidated Statements of Cash Flow - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Income (Loss)	$ 348,715	$ 336,752	$ 420,300
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income tax expense	12,895	14,383	40,805
(Accretion) amortization of investment (discounts) premiums, net	(67,702)	6,601	14,404
Gain on sales of investment securities, net	(13)	(2)	(8)
Provision (recapture) for credit losses	213,199	84,016	(42,651)
Change in cash surrender value of bank owned life insurance	(15,962)	(8,353)	(8,402)
Depreciation, amortization, and accretion	144,252	28,305	31,498
Gain on sale of premises and equipment	(31,472)	(2,747)	(574)
Additions to residential mortgage servicing rights carried at fair value	(5,347)	(24,137)	(38,522)
Change in fair value residential mortgage servicing rights carried at fair value	23,816	(37,265)	7,814
Stock-based compensation	18,073	9,753	10,906
Net (increase) decrease in equity and other investments	(448)	1,156	352
(Gain) loss on equity securities, net	(2,300)	7,099	1,511
(Gain) loss on sale of loans and leases, net	(10,200)	1,953	(145,723)
Change in fair value of loans held for sale	341	10,670	21,427
Origination of loans held for sale	(441,568)	(1,839,466)	(4,747,104)
Proceeds from sales of loans held for sale	602,634	2,076,548	4,952,918
Change in other assets and liabilities:
Net (increase) decrease in other assets	(24,163)	169,540	153,148
Net (decrease) increase in other liabilities	(94,910)	230,223	(9,376)
Net cash provided by operating activities	669,840	1,065,029	662,723
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investment securities available for sale	(926,216)	(276,812)	(1,838,923)
Proceeds from investment securities available for sale	1,694,850	396,100	761,249
Purchases of restricted equity securities	(290,817)	(180,543)	(53)
Redemption of restricted equity securities	260,697	144,315	30,803
Net change in loans and leases	(1,335,189)	(3,744,493)	(735,422)
Proceeds from sales of loans and leases	748,264	148,978	246,667
Proceeds from Sale of Property, Plant, and Equipment	40,688
Change in premises and equipment		(27,086)	(15,478)
Purchases of bank owned life insurance	(28,243)	0	0
Proceeds from bank owned life insurance death benefits	4,799	4,339	4,127
Proceeds from sale of mortgage servicing rights	(57,305)	0	0
Net cash received from sale of Umpqua Investments, Inc.	0	0	10,781
Payments for (Proceeds from) Businesses and Interest in Affiliates	(274,587)	0	0
Other	1,011	2,110	1,974
Net cash provided (used) in investing activities	501,736	(3,533,092)	(1,534,275)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net (decrease) increase in deposit liabilities	(651,130)	470,945	1,972,519
Net (decrease) increase in securities sold under agreements to repurchase	(126,675)	(183,478)	116,863
Increase (Decrease) in Federal Funds Purchased	14,000	0	0
Proceeds from borrowings	17,350,000	1,650,000	0
Repayment of borrowings	(16,586,522)	(750,000)	(765,000)
Net proceeds from issuance of common stock	1,185	54	34
Dividends paid on common stock	(270,261)	(182,273)	(183,734)
Repurchase and retirement of common stock	(6,282)	(4,163)	(80,690)
Net cash (used) provided by financing activities	(303,685)	1,001,085	1,059,992
Net increase (decrease) in cash and cash equivalents	867,891	(1,466,978)	188,440
Cash and cash equivalents, beginning of period	1,294,643	2,761,621	2,573,181
Cash and cash equivalents, end of period	2,162,534	1,294,643	2,761,621
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Interest	692,991	71,209	42,820
Income taxes	138,910	71,804	105,119
SUPPLEMENTAL DISCLOSURE OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Change in unrealized gains and losses on investment securities available for sale, net of taxes	80,800	(407,199)	(92,834)
Change in unrealized gains and losses on junior subordinated debentures carried at fair value, net of taxes	5,821	(21,424)	(28,152)
Transfer of loans to loans held for sale	118,085	0	0
Transfer of Loans Held-for-sale to Portfolio Loans	5,754	25,057	315,887
Umpqua Bank and Columbia Banking System Merger
Asset Acquisition [Line Items]
Assets acquired	19,230,586	0	0
Liabilities assumed	17,920,542	0	0
Net assets acquired	$ 1,310,044	$ 0	$ 0