Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 124,080	$ 93,531	$ 133,377	$ (14,038)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Accretion of investment discounts, net	(17,693)			(7,668)
Gain on sale of investment securities, net	(12)			0
Provision for credit losses	17,136			105,539
Change in cash surrender value of bank-owned life insurance	(4,672)			(491)
Depreciation, amortization and accretion	39,962			19,043
Gain on sale of premises and equipment	(183)			(305)
Additions to residential mortgage servicing rights carried at fair value	(1,237)			(1,601)
Change in fair value of residential mortgage servicing rights carried at fair value	36			7,818
Stock-based compensation	4,422			5,644
Net (increase) decrease in equity and other investments	(1,773)			131
Loss (gain) on equity securities, net	1,565			(2,416)
Gain on sale of loans and leases, net	(1,605)			(2,996)
Change in fair value of loans held for sale	(189)			(82)
Origination of loans held for sale	(86,903)			(131,726)
Proceeds from sales of loans held for sale	71,990			155,574
Change in other assets and liabilities:
Net increase in other assets	(38,767)			(51,404)
Net increase (decrease) in other liabilities	79,351			(119,989)
Net cash provided by (used in) operating activities	185,508			(38,967)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investment securities available for sale	(2,130)			(919,233)
Proceeds from investment securities available for sale	110,458			1,243,601
Purchases of restricted equity securities	(11,250)			(188,066)
Redemption of restricted equity securities	74,250			90,695
Net change in loans and leases	(263,625)			(59,389)
Proceeds from sales of loans and leases	18,980			20,502
Change in premises and equipment	5,899			3,486
Proceeds from bank-owned life insurance death benefits	1,160			2,028
Cash received in the Merger	0			274,587
Other	381			74
Net cash (used in) provided by investing activities	(77,675)			461,313
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase (decrease) in deposit liabilities	99,140			(672,737)
Net decrease in federal funds purchased	0			(14,000)
Net decrease in securities sold under agreements to repurchase	(38,546)			(107,747)
Proceeds from borrowings	3,900,000			5,945,000
Repayment of borrowings	(3,950,000)			(3,181,522)
Dividends paid on common stock	(74,997)			(45,582)
Repurchase and retirement of common stock	(4,847)			(5,216)
Net cash (used in) provided by financing activities	(69,250)			1,918,196
Net increase in cash and cash equivalents	38,583			2,340,542
Cash and cash equivalents, beginning of period	2,162,534		$ 3,635,185	1,294,643
Cash and cash equivalents, end of period	2,201,117	$ 2,162,534		3,635,185
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Interest	278,634			83,836
Income taxes	566			11,407
SUPPLEMENTAL DISCLOSURE OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Changes in unrealized gains and losses on investment securities available for sale, net of taxes	(90,778)			107,611
Changes in unrealized gains and losses on junior subordinated debentures carried at fair value, net of taxes	4,775			19,101
Umpqua Bank and Columbia Banking System Merger
Asset Acquisition [Line Items]
Assets acquired	0			19,226,816
Liabilities assumed	0			(17,919,326)
Net assets acquired	$ 0			$ 1,307,490