Debt - USD ($)				3 Months Ended							6 Months Ended
		Mar. 07, 2019	Aug. 06, 2018	Jun. 30, 2021		Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2021		Jun. 30, 2020	Dec. 18, 2019
Debt Instrument [Line Items]
Maximum hedging reserve				$ 1,000,000.0							$ 1,000,000.0
Unamortized Debt Issuance Costs				(30,400,000)			$ (26,500,000)				$ (30,400,000)
Percentage of collections on contributed loans											6.00%
Monthly servicing fee per financing											6.00%
Mortgage note	[1]			10,100,000			10,500,000				$ 10,100,000
Repayment of senior notes							148,200,000				0		$ 401,800,000
Senior notes				791,500,000			790,600,000				791,500,000
Loss on extinguishment of debt				0				$ 0	$ 7,400,000	$ 1,800,000	0		$ 7,400,000
Debt covenants				1							1
Carrying Amount				4,780,100,000			4,608,600,000				4,780,100,000
Senior Notes [Member]
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs				(8,500,000)			(9,400,000)				(8,500,000)
Carrying Amount				791,500,000			790,600,000				791,500,000
Mortgages [Member]
Debt Instrument [Line Items]
Debt facility financing amount			$ 12,000,000.0	12,000,000.0	[2]						12,000,000.0	[2]
Unamortized Debt Issuance Costs				0			0				0
Close date, secured financings			Aug. 06, 2018
Mortgage note				$ 10,100,000			$ 10,500,000				$ 10,100,000
Debt maturity date			Aug. 06, 2023								Aug. 06, 2023	[2]
Senior notes yield to maturity				1.59%			1.65%				1.59%
Carrying Amount				$ 10,100,000			$ 10,500,000				$ 10,100,000
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility	[3]			340,000,000.0							$ 340,000,000.0
Percentage of net book value of loans											80.00%
Unamortized Debt Issuance Costs	[3]			0			0				$ 0
Carrying Amount	[3]			0			$ 95,900,000				$ 0
Warehouse Facilities [Member]
Debt Instrument [Line Items]
Percentage of net book value of loans											80.00%
Number of warehouse facilities											6
Debt facility financing amount				1,250,000,000.0							$ 1,250,000,000.0
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2],[4]			$ 400,000,000.0							$ 400,000,000.0
Debt maturity date	[2],[5]										Apr. 30, 2024
Senior notes yield to maturity				0.00%			1.90%				0.00%
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Debt facility financing amount				$ 300,000,000.0	[2],[4]		$ 300,000,000.0				$ 300,000,000.0	[2],[4]
Debt maturity date	[2],[5]										Nov. 17, 2023
Senior notes yield to maturity				0.00%			0.00%				0.00%
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2],[4]			$ 125,000,000.0							$ 125,000,000.0
Debt maturity date	[2],[6]										Dec. 18, 2023
Senior notes yield to maturity				0.00%			0.00%				0.00%
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]			$ 75,000,000.0							$ 75,000,000.0
Debt maturity date	[2],[5]										Sep. 30, 2022
Senior notes yield to maturity				0.00%			0.00%				0.00%
Warehouse Facility VII [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2],[4]			$ 150,000,000.0							$ 150,000,000.0
Debt maturity date	[2],[7]										Dec. 16, 2021
Senior notes yield to maturity				0.00%			0.00%				0.00%
Term ABS 2017-3 [Member]
Debt Instrument [Line Items]
Senior notes yield to maturity				0.00%			3.41%				0.00%
Term ABS 2018-1 [Member]
Debt Instrument [Line Items]
Senior notes yield to maturity				0.00%			3.61%				0.00%
Term ABS 2018-2 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]			$ 450,000,000.0							$ 450,000,000.0
Debt financing close date											May 24, 2018
Debt maturity date	[2],[5]										May 15, 2020
Senior notes yield to maturity				4.11%			3.85%				4.11%
Net Book Value Of Loans Pledged As Collateral				$ 562,600,000							$ 562,600,000
Term ABS 2018-3 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]			$ 398,300,000							$ 398,300,000
Debt financing close date											Aug. 23, 2018
Debt maturity date	[2],[5]										Aug. 17, 2020
Senior notes yield to maturity				3.98%			3.78%				3.98%
Net Book Value Of Loans Pledged As Collateral				$ 500,100,000							$ 500,100,000
Term ABS 2019-1 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]			$ 402,500,000							$ 402,500,000
Debt financing close date											Feb. 21, 2019
Debt maturity date	[2],[5]										Feb. 15, 2021
Senior notes yield to maturity				3.61%			3.53%				3.61%
Net Book Value Of Loans Pledged As Collateral				$ 503,100,000							$ 503,100,000
Term ABS 2019-2 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]			$ 500,000,000.0							$ 500,000,000.0
Debt financing close date											Aug. 28, 2019
Debt maturity date	[2],[8]										Aug. 15, 2022
Senior notes yield to maturity				3.13%			3.13%				3.13%
Net Book Value Of Loans Pledged As Collateral				$ 625,100,000							$ 625,100,000
Term ABS 2019-3 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]			$ 351,700,000							$ 351,700,000
Debt financing close date											Nov. 21, 2019
Debt maturity date	[2],[5]										Nov. 15, 2021
Senior notes yield to maturity				2.56%			2.56%				2.56%
Net Book Value Of Loans Pledged As Collateral				$ 439,600,000							$ 439,600,000
Term ABS 2020-1 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]			$ 500,000,000.0							$ 500,000,000.0
Debt financing close date											Feb. 20, 2020
Debt maturity date	[2],[5]										Feb. 15, 2022
Senior notes yield to maturity				2.18%			2.18%				2.18%
Net Book Value Of Loans Pledged As Collateral				$ 625,100,000							$ 625,100,000
Term ABS 2020-2 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]			$ 481,800,000							$ 481,800,000
Debt financing close date											Jul. 23, 2020
Debt maturity date	[2],[9]										Jul. 15, 2022
Senior notes yield to maturity				1.65%			1.65%				1.65%
Net Book Value Of Loans Pledged As Collateral				$ 602,300,000							$ 602,300,000
2021 Senior Notes [Member]
Debt Instrument [Line Items]
Debt facility financing amount														$ 300,000,000.0
Repayment of senior notes						$ 151,800,000
Senior notes yield to maturity														6.125%
2024 Senior Notes [Member]
Debt Instrument [Line Items]
Debt facility financing amount				400,000,000.0							$ 400,000,000.0
Debt maturity date											Dec. 31, 2024
Senior notes				$ 400,000,000.0			$ 400,000,000.0				$ 400,000,000.0			$ 400,000,000.0
Senior notes yield to maturity				5.125%			5.125%				5.125%			5.125%
2026 Senior Notes [Member]
Debt Instrument [Line Items]
Debt facility financing amount		$ 400,000,000.0		$ 400,000,000.0							$ 400,000,000.0
Close date, secured financings		Mar. 07, 2019
Senior notes stated interest rate		6.625%
Debt maturity date		Mar. 15, 2026									Mar. 15, 2026
Senior notes				$ 400,000,000.0			$ 400,000,000.0				$ 400,000,000.0
Senior notes yield to maturity				6.625%			6.625%				6.625%
2023 Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes						$ 250,000,000.0
Senior notes yield to maturity														7.375%
LIBOR [Member] | Mortgages [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	[2],[4]										150.00%
LIBOR [Member] | Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate											187.50%
LIBOR [Member] | Warehouse Facility II [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	[2],[4]										175.00%
LIBOR [Member] | Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	[2],[4]										210.00%
LIBOR [Member] | Warehouse Facility V [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	[2],[4]										225.00%
LIBOR [Member] | Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	[2]										200.00%
Prime Rate [Member] | Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate											87.50%

[1] Measured at amortized cost with fair value disclosed.

[2] Financing made available only to a specified subsidiary of the Company.

[3] Excludes deferred debt issuance costs of $2.5 million and $3.2 million as of June 30, 2021 and December 31, 2020, respectively, which are included in other assets.

[4] Interest rate cap agreements are in place to limit the exposure to increasing interest rates

[5] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date based on the cash flows of the pledged assets.

[6] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date and any amounts remaining on December 16, 2025 will be due on that date.

[7] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date and any amounts remaining on December 16, 2023 will be due on that date.

[8] Represents the revolving maturity date. The Company has the option to redeem and retire the indebtedness after the revolving maturity date. If we do not elect this option, the outstanding balance will amortize based on the cash flows of the pledged assets.

[9] The Dealer Loans amount represents advances paid to Dealers on Consumer Loans assigned under our Portfolio Program. The Purchased Loans amount represents one-time payments made to Dealers to purchase Consumer Loans assigned under our Purchase Program.