Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022
CASH FLOWS FROM OPERATING ACTIVITIES:
Net (loss) income	$ (14,038)	$ 82,964	$ 78,591	$ 91,157
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
(Accretion) amortization of investment (discounts) premiums, net	(7,668)			1,106
Gain on sale of investment securities, net	0			(2)
Provision for credit losses	105,539			4,804
Change in cash surrender value of bank owned life insurance	(491)			(2,122)
Depreciation, amortization and accretion	19,043			7,613
Gain on sale of premises and equipment	(305)			(571)
Additions to residential mortgage servicing rights carried at fair value	(1,601)			(7,390)
Change in fair value of residential mortgage servicing rights carried at fair value	7,818			(34,802)
Stock-based compensation	5,644			2,454
Net decrease (increase) in equity and other investments	131			(413)
(Gain) loss on equity securities, net	(2,416)			2,661
Gain on sale of loans and leases, net	(2,996)			(4,458)
Change in fair value of loans held for sale	(82)			11,055
Origination of loans held for sale	(131,726)			(649,122)
Proceeds from sales of loans held for sale	155,574			683,347
Change in other assets and liabilities:
Net (increase) decrease in other assets	(51,404)			167,911
Net (decrease) increase in other liabilities	(119,989)			2,097
Net cash (used in) provided by operating activities	(38,967)			275,325
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investment securities available for sale	(919,233)			(131,869)
Proceeds from investment securities available for sale	1,243,601			126,011
Purchases of restricted equity securities	(188,066)			0
Redemption of restricted equity securities	90,695			28
Net change in loans and leases	(59,389)			(470,337)
Proceeds from sales of loans and leases	20,502			44,549
Change in premises and equipment	(3,486)			(3,736)
Proceeds from bank owned life insurance death benefits	2,028			1,111
Cash received in the Merger	274,587			0
Other	74			104
Net cash provided by (used in) investing activities	461,313			(434,139)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net (decrease) increase in deposit liabilities	(672,737)			104,906
Net decrease in federal funds purchased	(14,000)			0
Net (decrease) increase in securities sold under agreements to repurchase	(107,747)			7,292
Proceeds from borrowings	5,945,000			0
Repayment of borrowings	(3,181,522)			0
Dividends paid on common stock	(45,582)			(45,532)
Repurchase and retirement of common stock	(5,216)			(4,037)
Net cash provided by financing activities	1,918,196			62,629
Net increase (decrease) in cash and cash equivalents	2,340,542			(96,185)
Cash and cash equivalents, beginning of period	1,294,643		$ 2,665,436	2,761,621
Cash and cash equivalents, end of period	3,635,185	$ 1,294,643		2,665,436
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Interest	83,836			7,667
Income taxes	11,407			6,051
SUPPLEMENTAL DISCLOSURE OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Changes in unrealized gains and losses on investment securities available for sale, net of taxes	107,611			(176,079)
Changes in unrealized gains and losses on junior subordinated debentures carried at fair value, net of taxes	19,101			(9,436)
Net change in pension plan liability adjustment	18			0
Umpqua Bank and Columbia Banking System Merger
Asset Acquisition [Line Items]
Assets acquired	19,226,816			0
Liabilities assumed	(17,919,326)			0
Net assets acquired	$ 1,307,490			$ 0