Long-Term Debt - Narrative (Details)			1 Months Ended	12 Months Ended
	Mar. 05, 2021 USD ($)	Jun. 05, 2019 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2021 USD ($) termExtensionOption Rate	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2021 Rate
Debt Instrument [Line Items]
Cash sweeping event | Rate				175.00%
Rapid amortization event | Rate				120.00%
Manager termination event | Rate				120.00%
Interest-only debt service coverage ratio, default event | Rate				110.00%
Debt service coverage ratio | Rate				470.00%
Repayment of line of credit				$ 220,000,000	$ 0	$ 25,000,000
Gain (loss) on extinguishment of debt				0	0	(8,276,000)
Debt issuance costs				$ 7,400,000	11,800,000
2019 Class A-2 Notes
Debt Instrument [Line Items]
Covenant compliance, leverage ratio, maximum | Rate				525.00%			525.00%
Ratio of indebtedness to net capital | Rate				386.00%
Repayments of debt, principle				$ 9,750,000
Amortization of financing costs				2,200,000	2,100,000	1,200,000
Debt issuance costs, gross				12,900,000
Debt issuance costs				7,400,000
Debt instrument, periodic payment, principal				3,250,000
Debt instrument, annual principal payment				$ 13,000,000
2019 Class A-2-I Notes
Debt Instrument [Line Items]
Debt interest rate (percent)		4.194%		4.194%
Debt instrument, face amount		$ 700,000,000
Debt instrument, make-whole premium				$ 10,000,000
Additional interest on fixed rate		5.00%
Debt instrument, term		10 years
2019 Class A-2-I Notes | US Treasury (UST) Interest Rate
Debt Instrument [Line Items]
Basis spread on variable rate		2.15%
2019 Class A-2-II Notes
Debt Instrument [Line Items]
Debt interest rate (percent)		4.723%		4.723%
Debt instrument, face amount		$ 600,000,000
Debt instrument, make-whole premium				$ 39,000,000
2019 Class A-2-II Notes | US Treasury (UST) Interest Rate
Debt Instrument [Line Items]
Basis spread on variable rate		2.64%
2019 Class A-1 Notes
Debt Instrument [Line Items]
Debt interest rate (percent)				2.42%
2019 Class A-1 Notes | Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, term				5 years
Line of credit facility, maximum borrowing capacity				$ 225,000,000
Line of credit facility, commitment fee percentage				0.50%
Number of extensions | termExtensionOption				2
Extension period				1 year
Proceeds from long-term lines of credit			$ 220,000,000
Repayment of line of credit	$ 220,000,000
Maximum amount outstanding during period				$ 220,000,000
Line of credit facility, amount outstanding				$ 0
Debt, weighted average interest rate				2.42%
Debt instrument, collateral amount				$ 3,300,000
Line of credit facility, current borrowing capacity				221,700,000
Amortization of financing costs				600,000	600,000	800,000
Debt issuance costs				$ 1,500,000
Debt issuance costs, net					2,200,000
2019 Class A-1 Notes | Revolving Credit Facility | Eurodollar
Debt Instrument [Line Items]
Basis spread on variable rate				2.15%
2019 Class A-1 Notes | Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate				2.15%
Line of credit facility, percentage of advances drawn				60.00%
2019 Class A-1 Notes | Revolving Credit Facility | Commercial Paper Funding Rate Of Conduit Investor
Debt Instrument [Line Items]
Basis spread on variable rate				2.15%
Line of credit facility, percentage of advances drawn				40.00%
2019 Class A-1 Notes | Letter of Credit
Debt Instrument [Line Items]
Basis spread on variable rate				2.15%
Number of extensions | termExtensionOption				2
Extension period				1 year
2019 Class A-1 Notes | Letter of Credit | Eurodollar
Debt Instrument [Line Items]
Basis spread on variable rate				1.00%
2019 Class A-1 Notes | Letter of Credit | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate				1.15%
2019 Class A-1 Notes | Letter of Credit | Fed Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate				0.50%
2018-1 Class A-1 Notes
Debt Instrument [Line Items]
Debt issuance costs, gross						200,000
Debt issuance costs						$ 2,800,000
2014 Class A-2 Notes
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt				$ (8,300,000)
Amortization of financing costs					$ 1,400,000