INVESTMENT SECURITIES - Summary of Amortized Cost and Approximate Fair Value of Investment Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,488,717		$ 2,524,663
Allowance for Credit Losses	(4,639)	$ (5,339)	(3,952)	$ (3,849)	$ (3,439)	$ (578)
Gross Unrealized Gains	9,314		1,296
Gross Unrealized Losses	(115,659)		(145,147)
Fair Value	2,377,733		2,376,860
Equity securities	34,336		28,780
Total investment securities, at fair value	2,412,069		2,405,640
Available-for-sale debt securities, accrued interest	19,400		14,700
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40,179		97,359
Allowance for Credit Losses	(307)	(367)	(483)	(1,755)	(1,563)	(578)
Gross Unrealized Gains	0		15
Gross Unrealized Losses	(2,202)		(4,262)
Fair Value	37,670		92,629
Agency-guaranteed residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	216,821
Allowance for Credit Losses	0
Gross Unrealized Gains	4,357
Gross Unrealized Losses	0
Fair Value	221,178
Agency-guaranteed residential collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	201,529		129,589
Allowance for Credit Losses	0		0
Gross Unrealized Gains	1,277		0
Gross Unrealized Losses	(7,933)		(12,681)
Fair Value	194,873		116,908
Agency-guaranteed commercial collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	96,200
Allowance for Credit Losses	0
Gross Unrealized Gains	1,361
Gross Unrealized Losses	(618)
Fair Value	96,943
Collateralized loan obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	315,096		500,109
Allowance for Credit Losses	0		0
Gross Unrealized Gains	100		1
Gross Unrealized Losses	(4,767)		(11,018)
Fair Value	310,429		489,092
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	78,711		125,885
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(1,637)		(4,249)
Fair Value	77,074		121,636
Corporate notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	660,626		636,880
Allowance for Credit Losses	(4,332)	$ (4,972)	(3,469)	$ (2,094)	$ (1,876)	$ 0
Gross Unrealized Gains	646		79
Gross Unrealized Losses	(61,969)		(50,456)
Fair Value	594,971		583,034
Private label collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	879,555		1,034,841
Allowance for Credit Losses	0		0
Gross Unrealized Gains	1,573		1,201
Gross Unrealized Losses	(36,533)		(62,481)
Fair Value	$ 844,595		$ 973,561