Debt - Additional Information (Detail) - USD ($)		1 Months Ended										3 Months Ended
	Oct. 01, 2022	Feb. 28, 2023	Nov. 30, 2022	Oct. 30, 2022	Sep. 30, 2022	Feb. 28, 2022	Oct. 31, 2021	Jul. 31, 2021	Apr. 30, 2021	Feb. 28, 2021	Sep. 30, 2020	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Line of Credit Facility [Line Items]
Cash												$ 7,108,000	$ 17,635,000	$ 3,873,000
Cash deposited to restricted cash reserve account												127,178,000	138,919,000	127,926,000
Advances on securitizations												0	$ 250,000,000
RMR II revolving warehouse credit facility
Line of Credit Facility [Line Items]
Secured line of credit									$ 125,000,000			$ 75,000,000
Percentage of advances on debt agreement eligible secured finance receivables									80.00%			83.00%
Interest rate, basis spread									2.15%
Debt revolving period end date												2023-03
Debt maturity date												2024-03
Debt Instrument, Description of Variable Rate Basis												which borrowings under the facility bore interest, payable monthly, at a rate equal to three-month LIBOR, with a LIBOR floor of 0.25%, plus a blended margin of 2.35% (2.15% prior to the April 2021 amendment).
RMR III revolving warehouse credit facility
Line of Credit Facility [Line Items]
Advances on securitizations												$ 16,300,000
RMR IV revolving warehouse credit facility
Line of Credit Facility [Line Items]
Secured line of credit												$ 125,000,000
Percentage of advances on debt agreement eligible secured finance receivables												81.00%
Credit facility, eligible borrowing capacity												$ 22,900,000
Effective interest rate												7.12%
Cash deposited to restricted cash reserve account												$ 300,000
Debt revolving period end date												2023-04
Debt maturity date												2024-04
Line of credit facility, description												The facility was to convert to an amortizing loan in April 2023 and terminates in April 2024. The debt is secured by finance receivables and other related assets that the Company purchased from its affiliates, which the Company then sold and transferred to RMR IV. Advances on the facility are capped at 81% of eligible finance receivables
RMR V revolving warehouse credit facility
Line of Credit Facility [Line Items]
Secured line of credit												$ 100,000,000
Percentage of advances on debt agreement eligible secured finance receivables												80.00%
Credit facility, eligible borrowing capacity												$ 20,100,000
Effective interest rate												7.87%
Cash deposited to restricted cash reserve account												$ 500,000
Line of credit facility, description												amended and restated the credit agreement that provides for a $100 million revolving warehouse credit facility to RMR V to extend the date at which the facility converts to an amortizing loan and the termination date to November 2022 and November 2023, respectively (October 2022 and October 2023, respectively, prior to the September 2022 amendment). Following a subsequent amendment in November 2022, the amortizing loan conversion date and termination date were extended to November 2024 and November 2025, respectively. The debt is secured by finance receivables and other related assets that the Company purchased from its affiliates, which the Company then sold and transferred to RMR V. Advances on the facility are capped at 80% of eligible finance receivables.
Line of credit facility, interest rate description												Borrowings under the facility bear interest, payable monthly, at a per annum rate, which in the case of a conduit lender is the commercial paper rate, plus a margin of 2.75% (2.20% prior to the November 2022 amendment). The effective interest rate was 7.87% as of March 31, 2023. RMR V pays an unused commitment fee between 0.45% and 0.75% based upon the average daily utilization of the facility. RMR V had $20.1 million of immediate availability to draw down cash under the facility and held $0.5 million in restricted cash reserves as of March 31, 2023 to satisfy provisions of the credit agreement.
RMR VI revolving warehouse credit facility
Line of Credit Facility [Line Items]
Secured line of credit		$ 75,000,000
Percentage of advances on debt agreement eligible secured finance receivables		80.00%
Credit facility, eligible borrowing capacity												$ 100,000
Effective interest rate		7.27%
Interest rate, during revolving period		0.00%
Unused line fee		0.50%
Cash deposited to restricted cash reserve account												$ 200,000
Line of credit facility, description		The facility converts to an amortizing loan in February 2025 and terminates in February 2026. The debt is secured by finance receivables and other related assets that the Company purchased from its affiliates, which the Company then sold and transferred to RMR VI. Advances on the facility are capped at 80% of eligible finance receivables.
Line of credit facility, interest rate description		Borrowings under the facility bear interest, payable monthly, at a rate equal to one-month SOFR, plus (i) 0.10% per annum, (ii) a margin of 2.50%, and (iii) the applicable step-up margin (0.00% during the revolving period). The effective interest rate was 7.27% as of March 31, 2023. RMR VI pays a monthly unused commitment fee of 0.50%. RMR VI had $0.1 million of immediate availability to draw down cash under the facility and held $0.2 million in restricted cash reserves as of March 31, 2023 to satisfy provisions of the credit agreement.
RMIT 2020-1 securitization
Line of Credit Facility [Line Items]
Effective interest rate												2.85%
Cash deposited to restricted cash reserve account												$ 1,900,000
Debt revolving period end date												2023-09
Debt maturity date												2030-10
Advances on securitizations											$ 180,000,000
Debt Instrument, Payment Terms												Prior to maturity in October 2030, the Company may redeem the notes in full, but not in part, at its option on any business day on or after the payment date occurring in October 2023. No payments of principal of the notes will be made during the revolving period
RMIT 2021-1 securitization
Line of Credit Facility [Line Items]
Effective interest rate												2.08%
Cash deposited to restricted cash reserve account												$ 2,600,000
Debt revolving period end date												2024-02
Debt maturity date												2031-03
Advances on securitizations										$ 249,000,000
Debt Instrument, Payment Terms												Prior to maturity in March 2031, the Company may redeem the notes in full, but not in part, at its option on any business day on or after the payment date occurring in March 2024. No payments of principal of the notes will be made during the revolving period
RMIT 2021-2 securitization
Line of Credit Facility [Line Items]
Effective interest rate												2.30%
Cash deposited to restricted cash reserve account												$ 2,100,000
Debt revolving period end date												2026-07
Debt maturity date												2033-08
Advances on securitizations								$ 200,000,000
Debt Instrument, Payment Terms												Prior to maturity in August 2033, the Company may redeem the notes in full, but not in part, at its option on any business day on or after the payment date occurring in August 2026. No payments of principal of the notes will be made during the revolving period
RMIT 2021-3 securitization
Line of Credit Facility [Line Items]
Effective interest rate												3.88%
Cash deposited to restricted cash reserve account												$ 1,500,000
Debt revolving period end date												2026-09
Debt maturity date												2033-10
Advances on securitizations							$ 125,000,000
Debt Instrument, Payment Terms												Prior to maturity in October 2033, the Company may redeem the notes in full, but not in part, at its option on any business day on or after the payment date occurring in October 2024. No payments of principal of the notes will be made during the revolving period.
RMIT 2022-1 securitization
Line of Credit Facility [Line Items]
Effective interest rate												3.59%
Cash deposited to restricted cash reserve account												$ 2,600,000
Debt revolving period end date												2025-02
Debt maturity date												2032-03
Advances on securitizations						$ 250,000,000
Debt Instrument, Payment Terms												Prior to maturity in March 2032, the Company may redeem the notes in full, but not in part, at its option on any note payment date on or after the payment date occurring in March 2025. No payments of principal of the notes will be made during the revolving period.
RMIT 2022-2B securitization
Line of Credit Facility [Line Items]
Effective interest rate												7.51%
Cash deposited to restricted cash reserve account												$ 2,300,000
Debt revolving period end date												2024-10
Debt maturity date												2031-11
Advances on securitizations				$ 200,000,000
Debt Instrument, Payment Terms												Prior to maturity in November 2031, the Company may redeem the notes in full, but not in part, at its option on any note payment date on or after the payment date occurring in November 2024. No payments of principal of the notes will be made during the revolving period.
Contractual Priority Payments [Member]
Line of Credit Facility [Line Items]
Cash deposited to restricted cash reserve account												$ 112,600,000		$ 112,200,000
Minimum [Member] | RMR IV revolving warehouse credit facility
Line of Credit Facility [Line Items]
Unused line fee												0.35%
Minimum [Member] | RMR V revolving warehouse credit facility
Line of Credit Facility [Line Items]
Interest rate, basis spread			2.20%
Unused line fee												0.45%
Debt revolving period end date					2022-11
Debt maturity date			2024-11
Maximum [Member] | RMR IV revolving warehouse credit facility
Line of Credit Facility [Line Items]
Unused line fee												0.70%
Maximum [Member] | RMR V revolving warehouse credit facility
Line of Credit Facility [Line Items]
Interest rate, basis spread			2.75%
Unused line fee												0.75%
Debt revolving period end date					2023-11
Debt maturity date			2025-11
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | RMR II revolving warehouse credit facility
Line of Credit Facility [Line Items]
Effective interest rate	0.25%
Interest rate, basis spread	2.35%
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | RMR IV revolving warehouse credit facility
Line of Credit Facility [Line Items]
Interest rate, basis spread	2.35%
Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | RMR VI revolving warehouse credit facility
Line of Credit Facility [Line Items]
Effective interest rate		0.10%
Interest rate, basis spread		2.50%
London Interbank Offered Rate (LIBOR) [Member] | RMR II revolving warehouse credit facility
Line of Credit Facility [Line Items]
Effective interest rate									0.25%
Senior Revolving Credit Facility | Unrestricted Cash [Member]
Line of Credit Facility [Line Items]
Cash												$ 7,100,000
Senior Revolving Credit Facility | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Line of Credit Facility [Line Items]
Interest rate, basis spread	3.00%
Senior Revolving Credit Facility | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate | Minimum [Member]
Line of Credit Facility [Line Items]
Effective interest rate	0.50%
Debt Instrument Variable Rate Base Condition Two | London Interbank Offered Rate (LIBOR) [Member] | RMR II revolving warehouse credit facility
Line of Credit Facility [Line Items]
Interest rate, basis spread												2.35%
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Commitment fee description												The Company pays an unused commitment fee between 0.50% and 1.00% based upon the average outstanding balance.
Effective interest rate												7.77%
Revolving Credit Facility [Member] | Senior Revolving Credit Facility Prior To November Thirty Two Thousand Twenty Two
Line of Credit Facility [Line Items]
Secured line of credit			$ 500,000,000
Revolving Credit Facility [Member] | Senior Revolving Credit Facility
Line of Credit Facility [Line Items]
Secured line of credit			$ 420,000,000
Debt agreement expiration date												Sep. 30, 2024
Percentage of advances on debt agreement eligible secured finance receivables												83.00%
Current percentage of advances on eligible secured finance receivables												81.00%
Credit facility, eligible borrowing capacity												$ 131,900,000
Revolving Credit Facility [Member] | Senior Revolving Credit Facility | Minimum [Member]
Line of Credit Facility [Line Items]
Unused line fee												0.50%
Revolving Credit Facility [Member] | Senior Revolving Credit Facility | Maximum [Member]
Line of Credit Facility [Line Items]
Unused line fee												1.00%