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 (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	$ 4,505,816	$ 4,850,302
Allowance for loan and lease losses	(259,150)	(310,387)	$ (348,857)	$ (327,852)
Loans and leases held for investment, net	4,246,666	4,539,915
Loans pledged as collateral under the FRB discount window	3,000,000	3,500,000
Assets Pledged As Collateral
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment, net	479,600	479,000
Consumer
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	3,831,791	4,159,919
Allowance for loan and lease losses	(246,280)	(298,061)	(333,546)	(312,489)
Consumer | Unsecured personal
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	3,397,853	3,726,830
Consumer | Residential mortgages
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	180,697	183,050
Consumer | Secured consumer
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	253,241	250,039
Commercial
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	674,025	690,383
Allowance for loan and lease losses	(12,870)	(12,326)	$ (15,311)	$ (15,363)
Commercial | Equipment finance
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	101,902	110,992
Commercial | Commercial real estate
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	376,022	380,322
Commercial | Commercial and industrial
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans and leases held for investment	$ 196,101	$ 199,069