Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 255,184	$ 253,788
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
(Accretion) amortization of investment (discounts) premiums, net	(47,972)	5,089
Gain on sale of investment securities, net	(4)	(2)
Provision for credit losses	158,290	51,068
Change in cash surrender value of bank owned life insurance	(11,484)	(6,293)
Depreciation, amortization and accretion	102,409	21,560
Gain on sale of premises and equipment	(27,438)	(2,203)
Additions to residential mortgage servicing rights carried at fair value	(4,427)	(20,397)
Change in fair value of residential mortgage servicing rights carried at fair value	14,350	(52,165)
Stock-based compensation	13,317	7,254
Net decrease in equity and other investments	273	1,554
Loss on equity securities, net	336	7,383
(Gain) loss on sale of loans and leases, net	(7,715)	207
Change in fair value of loans held for sale	1,118	14,616
Origination of loans held for sale	(354,535)	(1,622,633)
Proceeds from sales of loans held for sale	485,761	1,793,676
Change in other assets and liabilities:
Net (increase) decrease in other assets	(26,185)	203,802
Net increase in other liabilities	26,191	248,362
Net cash provided by operating activities	577,469	904,666
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investment securities available for sale	(920,899)	(175,656)
Proceeds from investment securities available for sale	1,552,199	328,685
Purchases of restricted equity securities	(238,066)	(164,344)
Redemption of restricted equity securities	218,696	134,267
Net change in loans and leases	(991,404)	(3,064,741)
Proceeds from sales of loans and leases	701,647	111,584
Change in premises and equipment	(44,055)	11,259
Proceeds from bank owned life insurance death benefits	3,020	4,069
Proceeds from sale of mortgage servicing rights	57,454	0
Cash received in the Merger	274,587	0
Other	468	1,997
Net cash provided by (used in) investing activities	701,757	(2,835,398)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net (decrease) increase in deposit liabilities	(633,969)	222,437
Net decrease in federal funds purchased	(14,000)	0
Net decrease in securities sold under agreements to repurchase	(120,411)	(108,678)
Proceeds from borrowings	12,100,000	750,000
Repayment of borrowings	(11,301,522)	0
Net proceeds from issuance of common stock	1,185	54
Dividends paid on common stock	(195,351)	(136,693)
Repurchase and retirement of common stock	(6,106)	(4,150)
Net cash (used in) provided by financing activities	(170,174)	722,970
Net increase (decrease) in cash and cash equivalents	1,109,052	(1,207,762)
Cash and cash equivalents, beginning of period	1,294,643	2,761,621
Cash and cash equivalents, end of period	2,403,695	1,553,859
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Interest	456,797	33,154
Income taxes	80,226	44,174
SUPPLEMENTAL DISCLOSURE OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Changes in unrealized gains and losses on investment securities available for sale, net of taxes	(247,397)	(427,691)
Changes in unrealized gains and losses on junior subordinated debentures carried at fair value, net of taxes	(6,292)	(23,628)
Net change in pension plan liability adjustment	124	0
Transfer of loans to loans held for sale	118,085	0
Umpqua Bank and Columbia Banking System Merger
Asset Acquisition [Line Items]
Assets acquired	19,230,586	0
Liabilities assumed	(17,920,542)	0
Net assets acquired	$ 1,310,044	$ 0