Long-Term Debt - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Cash deposited to restricted cash reserve account	$ 54,649,000	$ 54,164,000		$ 38,917,000	$ 46,484,000
Unrestricted cash	14,668,000	2,263,000		$ 2,331,000	$ 3,657,000
Unrestricted Cash [Member]
Line of Credit Facility [Line Items]
Unrestricted cash	14,700,000
Revolving Warehouse Credit Facility [Member]
Line of Credit Facility [Line Items]
Secured line of credit	$ 125,000,000
Debt agreement expiration date	Sep. 20, 2022
Line of credit facility, accordion feature	$ 150,000,000
Percentage of advances on debt agreement eligible secured finance receivables	80.00%
Cash deposited to restricted cash reserve account	$ 1,000,000
Debt maturity date	2022-04
Debt revolving period end date	2021-04
RMIT 2018-1 securitization [Member]
Line of Credit Facility [Line Items]
Cash deposited to restricted cash reserve account	$ 1,700,000
Debt maturity date	2027-07
Terms related to loan prepayment	Prior to maturity in July 2027, 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 July 2020. No payments of principal of the notes will be made during the revolving period.
Debt revolving period end date	2020-06
Private offering of investment grade asset-backed notes	$ 150,000,000
Weighted average rate	3.93%
RMIT 2018-2 securitization [Member]
Line of Credit Facility [Line Items]
Cash deposited to restricted cash reserve account	$ 1,400,000
Debt maturity date	2028-01
Terms related to loan prepayment	Prior to maturity in January 2028, 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 January 2021. No payments of principal of the notes will be made during the revolving period.
Debt revolving period end date	2020-12
Private offering of investment grade asset-backed notes	$ 130,000,000
Weighted average rate	4.87%
RMIT 2019-1 securitization [Member]
Line of Credit Facility [Line Items]
Cash deposited to restricted cash reserve account	$ 1,400,000
Debt maturity date	2028-11
Terms related to loan prepayment	Prior to maturity in November 2028, 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 2021. No payments of principal of the notes will be made during the revolving period.
Debt revolving period end date	2021-10
Private offering of investment grade asset-backed notes	$ 130,000,000
Weighted average rate	3.17%
Senior Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Secured line of credit	$ 640,000,000
Debt agreement expiration date	Jun. 20, 2020
Line of credit facility, accordion feature	$ 650,000,000
Percentage of advances on debt agreement eligible secured finance receivables	85.00%
Percentage of advances on debt agreement eligible unsecured finance receivables	80.00%
Current percentage of advances on eligible secured finance receivables	77.00%
Current percentage of advances on eligible unsecured finance receivables	72.00%
Credit facility, eligible borrowing capacity	$ 87,600,000
Description of Variable Rate Basis	Borrowings under the facility bear interest, payable monthly, at a blended rate equal to three-month LIBOR, plus a margin of 2.15% (2.20% prior to the October 2019 amendment). The three-month LIBOR was 1.45% and 1.91% at March 31, 2020 and December 31, 2019, respectively. RMR II pays an unused commitment fee between 0.35% and 0.85% based upon the average daily utilization of the facility.
Percentage of advances on debt agreement eligible delinquent renewals of finance receivables	60.00%
Commitment fee description	The Company pays an unused line fee between 0.375% and 0.65% based upon the average outstanding balance of the facility.
Current percentage of advances on eligible delinquent renewals of finance receivables	52.00%
Senior Revolving Credit Facility [Member] | Senior Revolving Credit Facility Prior to September 20, 2019 [Member]
Line of Credit Facility [Line Items]
Secured line of credit	$ 638,000,000
Debt agreement expiration date	Jun. 20, 2020
Waterfall [Member]
Line of Credit Facility [Line Items]
Cash deposited to restricted cash reserve account	$ 38,500,000	$ 39,400,000
Minimum [Member] | Revolving Warehouse Credit Facility [Member]
Line of Credit Facility [Line Items]
Unused line fee	0.35%
Minimum [Member] | Senior Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Unused line fee	0.375%
Maximum [Member] | Revolving Warehouse Credit Facility [Member]
Line of Credit Facility [Line Items]
Unused line fee	0.85%
Maximum [Member] | Senior Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Unused line fee	0.65%
London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Interest rate	0.99%	1.76%
London Interbank Offered Rate (LIBOR) [Member] | Revolving Warehouse Credit Facility [Member]
Line of Credit Facility [Line Items]
Interest rate	1.45%	1.91%
London Interbank Offered Rate (LIBOR) [Member] | Revolving Warehouse Credit Facility [Member] | Milestones Associated with Conversion to New Loan Origination and Servicing System [Member]
Line of Credit Facility [Line Items]
Interest rate, basis spread		2.15%	2.20%
London Interbank Offered Rate (LIBOR) [Member] | Senior Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Interest rate, basis spread	3.00%
Interest rate	0.99%	1.76%
London Interbank Offered Rate (LIBOR) [Member] | Senior Revolving Credit Facility [Member] | Availability Percentage Below 10% [Member]
Line of Credit Facility [Line Items]
Interest rate, basis spread	3.25%
London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member] | Senior Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Effective interest rate on line of credit	1.00%