Loans and Leases Held for Investment at Amortized Cost, Net of Allowance For Loan and Lease Losses - Schedule of Components of Portfolio Segment by Class of Financing Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	$ 4,850,302	$ 5,033,154
Allowance for loan and lease losses	(310,387)	(327,852)	$ (144,389)	$ 0
Loans and leases held for investment, net	4,539,915	4,705,302
Charged-off	310,387	327,852	144,389	0
Loans pledged as collateral under the FRB discount window	$ 3,500,000	$ 283,600
Allowance ratios	6.40%	6.50%
Allowance for future estimated net charge-offs	$ 355,800	$ 340,400
Negative allowance for expected recoveries of amounts previously charged-off	45,400	12,500
Asset Pledged as Collateral
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net	479,000	156,200
Consumer Portfolio Segment
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	4,159,919	4,260,608
Allowance for loan and lease losses	(298,061)	(312,489)	(128,812)	0
Loans and leases held for investment, net	3,861,858	3,948,119
Charged-off	$ 298,061	$ 312,489	128,812	0
Allowance ratios	7.20%	7.30%
Consumer Portfolio Segment | Unsecured personal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	$ 3,726,830	$ 3,866,373
Consumer Portfolio Segment | Residential mortgages
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	183,050	199,601
Consumer Portfolio Segment | Secured consumer
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	250,039	194,634
Commercial Portfolio Segment
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	690,383	772,546
Allowance for loan and lease losses	(12,326)	(15,363)	(15,577)	0
Loans and leases held for investment, net	678,057	757,183
Charged-off	$ 12,326	$ 15,363	$ 15,577	$ 0
Allowance ratios	1.80%	2.00%
Commercial Portfolio Segment | Equipment finance
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	$ 110,992	$ 160,319
Commercial Portfolio Segment | Commercial real estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	380,322	373,501
Commercial Portfolio Segment | Commercial and industrial
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	199,069	238,726
Commercial Portfolio Segment | Commercial and industrial loan, PPP
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	$ 6,400	$ 67,000