Variable Interest Entities and Securitizations - Additional Information (Details) $ in Thousands		1 Months Ended	9 Months Ended	12 Months Ended
	Apr. 30, 2024 USD ($)	Jan. 31, 2023 USD ($)	Sep. 30, 2024 USD ($) Facility	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Variable Interest Entity [Line Items]
Beneficial interests in securitizations					$ 20,592
UACC
Variable Interest Entity [Line Items]
Risk retention rules percentage			5.00%
Number of senior secured warehouse credit facilities | Facility			4
Beneficial interests in securitizations			$ 2,600	$ 4,500
Net proceeds from securitization			297,200	$ 260,900
Collateralized finance receivable	$ 380,100	$ 326,400
UACC | Asset-backed Securities
Variable Interest Entity [Line Items]
Amount of rated asset-backed securities in an auto finance receivable securitization transaction, sold			300,000
UACC | Non-Investment Grade Securities
Variable Interest Entity [Line Items]
Non-investment grade securities, repurchased			4,200
Net payments to securitization			$ 4,800