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	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	$ 5,533,349		$ 5,033,154
Allowance for loan and lease losses	(355,163)	$ (348,857)	(327,852)	$ (243,260)	$ (187,985)	$ (144,389)
Loans and leases held for investment, net	5,178,186		4,705,302
Loans pledged as collateral under the FRB discount window	$ 4,800,000		$ 283,600
Allowance Ratios	6.40%		6.50%
Assets pledged as collateral
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net	$ 151,200		$ 156,200
Consumer Portfolio Segment
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	4,800,958		4,260,608
Allowance for loan and lease losses	(341,161)	(333,546)	(312,489)	(228,184)	(173,857)	(128,812)
Loans and leases held for investment, net	$ 4,459,797		$ 3,948,119
Allowance Ratios	7.10%		7.30%
Consumer Portfolio Segment | Unsecured personal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	$ 4,371,330		$ 3,866,373
Consumer Portfolio Segment | Residential mortgages
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	192,256		199,601
Consumer Portfolio Segment | Secured consumer
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	237,372		194,634
Commercial Portfolio Segment
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	732,391		772,546
Allowance for loan and lease losses	(14,002)	$ (15,311)	(15,363)	$ (15,076)	$ (14,128)	$ (15,577)
Loans and leases held for investment, net	$ 718,389		$ 757,183
Allowance Ratios	1.90%		2.00%
Commercial Portfolio Segment | Equipment finance
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	$ 142,073		$ 160,319
Commercial Portfolio Segment | Commercial real estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	382,738		373,501
Commercial Portfolio Segment | Commercial and industrial
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	207,580		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	$ 17,600		$ 67,000