Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
PacWest common stock issued	$ 0	$ 0
Cash flows from operating activities:
Net earnings	468,636	465,339	$ 357,818
Depreciation and amortization	39,115	35,168	32,029
Accretion (Amortization) of Discounts and Premiums, Investments	13,962	23,938	41,450
Customer related expense	18,726	22,506	14,240
Operating Lease, Right-of-Use Asset, Amortization	29,393	0	0
Provision for credit losses	22,000	45,000	57,752
Gain on sale of foreclosed assets, net	(3,689)	(609)	(871)
Provision for losses on foreclosed assets	78	74	2,138
Gain on sale of loans and leases, net	(1,114)	(4,675)	(6,197)
Loss (gain) on sale of premises and equipment	599	(20)	(386)
(Gain) loss on sale of securities, net	(25,445)	(8,176)	541
Gain (Loss) on Sale of Insurance Block	0	(1,338)	(1,050)
Unrealized gain on derivatives and foreign currencies, net	(228)	(325)	(429)
Earned stock compensation	26,815	29,768	25,568
Decrease (increase) in deferred income taxes, net	14,714	(136)	76,860
Decrease (increase) in other assets	15,547	25,117	(118,477)
(Decrease) increase in accrued interest payable and other liabilities	(36,449)	(23,604)	2,982
Net cash provided by operating activities	582,660	608,027	483,968
Cash flows from investing activities:
Cash acquired in acquisitions, net of cash consideration paid	0	0	160,318
Net increase in loans and leases	(1,005,478)	(1,209,986)	(1,303,752)
Proceeds from sales of loans and leases	102,573	646,587	1,322,456
Proceeds from maturities and paydowns of securities available-for-sale	325,863	290,177	435,925
Proceeds from sales of securities available-for-sale	1,584,860	571,800	759,300
Purchases of securities available-for-sale	(1,569,421)	(1,180,545)	(1,298,105)
Net (purchases) redemptions of Federal Home Loan Bank stock	(8,821)	(11,313)	12,982
Proceeds from sales of foreclosed assets	8,590	13,479	12,345
Purchases of premises and equipment, net	(15,104)	(12,385)	(7,919)
Proceeds from sales of premises and equipment	73	57	10,309
Proceeds from Life Insurance Policy	555	3,546	2,478
Net increase in equipment leased to others under operating leases	(54,996)	(28,610)	(73,596)
Net cash (used in) provided by investing activities	(631,306)	(917,193)	32,741
Cash flows from financing activities:
Net (decrease) increase in noninterest-bearing deposits	(643,530)	(615,263)	343,663
Net increase (decrease) in interest-bearing deposits	1,008,152	624,094	(63,700)
Net increase (decrease) in borrowings	387,894	903,772	(461,349)
Net decrease in subordinated debentures		(12,372)	0
Common stock repurchased and restricted stock surrendered		(315,542)	(109,153)
Cash dividends paid, net		(288,193)	(247,403)
Net cash provided by (used in) financing activities	300,503	296,496	(537,942)
Net increase (decrease) in cash and cash equivalents	251,857	(12,670)	(21,233)
Cash and cash equivalents, beginning of year	385,767	398,437	419,670
Cash and cash equivalents, end of year	637,624	385,767	398,437
Supplemental disclosures of cash flow information:
Cash paid for interest	200,463	119,042	69,477
Cash paid for income taxes	123,533	98,575	208,066
Real Estate Owned, Transfer to Real Estate Owned		16,914
Loans transferred to foreclosed assets	120	16,914	580
Transfer of Portfolio Loans and Leases to Held-for-sale	25,124	0	481,100
PacWest common stock issued	0	0
Parent [Member]
Cash flows from operating activities:
(Gain) loss on sale of securities, net	0	0	(15)
Earned stock compensation		29,768	25,568
Decrease (increase) in other assets	(35,510)	(36,362)	(34,274)
Cash flows from investing activities:
Cash acquired in acquisitions, net of cash consideration paid	0	0	(223,818)
Purchases of securities available-for-sale	0	0	426
Cash flows from financing activities:
Common stock repurchased and restricted stock surrendered	(162,965)	(315,542)	(109,153)
Cash dividends paid, net	(289,048)	(288,193)	(247,403)
Cash and cash equivalents, beginning of year	244,859	185,511	494,765
Cash and cash equivalents, end of year	$ 113,961	$ 244,859	185,511
CU Bancorp
Condensed Cash Flow Statements, Captions [Line Items]
PacWest common stock issued			446,233
Supplemental disclosures of cash flow information:
PacWest common stock issued			$ 446,233