Borrowings - Narrative (Details) $ / shares in Units, $ in Thousands, shares in Millions		1 Months Ended					12 Months Ended
	Aug. 20, 2021 USD ($) optionToExtend d $ / shares	Dec. 31, 2021 USD ($) $ / shares	Jun. 30, 2021 USD ($)	Oct. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Nov. 30, 2015 USD ($)	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019
Schedule of Borrowings [Line Items]
Repayments of debt							$ 71,316	$ 148,113	$ 109,939
Outstanding borrowings		$ 709,787					709,787	62,681
Purchase of capped calls							58,523	0	$ 0
Mezzanine Loan
Schedule of Borrowings [Line Items]
Aggregate principal amount				$ 15,000
Mezzanine Loan | Maximum
Schedule of Borrowings [Line Items]
Stated interest rate				10.00%
Term loan
Schedule of Borrowings [Line Items]
Repayments of debt			$ 15,000
Outstanding borrowings		0					0	15,000
UNI credit facility | Revolving credit facility
Schedule of Borrowings [Line Items]
Maximum borrowing capacity					$ 5,500
Repayments of credit facility			$ 5,500
Outstanding borrowings		$ 0					$ 0	$ 5,500
ULT Warehouse Credit Facility | Revolving credit facility
Schedule of Borrowings [Line Items]
Maximum borrowing capacity						$ 100,000
Redemption price (in percent)						100.00%
Minimum utilization requirement						$ 30,000
Maximum advance rate (in percent)		85.00%					85.00%	80.00%
UAWT Warehouse Credit Facility | Revolving credit facility
Schedule of Borrowings [Line Items]
Maximum borrowing capacity		$ 100,000					$ 100,000
Monthly unused fee (in percent)		0.50%
Maximum advance rate (in percent)		82.50%					82.50%
UAWT Warehouse Credit Facility | Minimum | Revolving credit facility
Schedule of Borrowings [Line Items]
Monthly unused fee (in percent)						0.10%
UAWT Warehouse Credit Facility | Maximum | Revolving credit facility
Schedule of Borrowings [Line Items]
Monthly unused fee (in percent)						1.00%
Risk retention funding loans
Schedule of Borrowings [Line Items]
Outstanding borrowings		$ 507					$ 507	$ 7,187
Assets pledged as collateral		4,800					4,800	12,600
2018-2 RR Financing Agreement
Schedule of Borrowings [Line Items]
Stated interest rate				4.00%
2019-2 RR Financing Agreement
Schedule of Borrowings [Line Items]
Stated interest rate										4.33%
Outstanding borrowings								6,600
2026 ("Notes")
Schedule of Borrowings [Line Items]
Outstanding borrowings		$ 661,250					661,250	$ 0
Purchase of capped calls							$ 58,500
Initial conversion price (in dollars per share) | $ / shares		$ 285.26					$ 285.26
Initial cap price (in dollars per share) | $ / shares		$ 400.36					$ 400.36
Capped call cover (in shares) | shares							2.3
2026 ("Notes") | Convertible Debt
Schedule of Borrowings [Line Items]
Aggregate principal amount	$ 661,300
Stated interest rate	0.25%
Additional aggregate principal	$ 86,300
Net proceeds from sale of the notes	$ 645,500
Initial conversion rate (in shares)	0.003506
Initial conversion price (in dollars per share) | $ / shares	$ 285.26
Percent of the principal amount	100.00%
2026 ("Notes") | Convertible Debt | Conversion Period One
Schedule of Borrowings [Line Items]
Trading days | d	20
Consecutive trading days | optionToExtend	30
Conversion price maximum threshold	130.00%
2026 ("Notes") | Convertible Debt | Conversion Period Two
Schedule of Borrowings [Line Items]
Trading days | optionToExtend	5
Consecutive trading days | optionToExtend	5
Percentage of the last reported sale price	98.00%
2026 ("Notes") | Convertible Debt | Conversion Period Three
Schedule of Borrowings [Line Items]
Redemption price (in percent)	100.00%
Trading days | d	20
Consecutive trading days | d	30
Conversion price maximum threshold	130.00%
Gross debt issuance cost		$ 15,700					$ 15,700
Coupon interest expense							600
Amortization of debt issuance costs							$ 1,400
Effective interest rate		0.70%					0.70%
Prime Rate | Mezzanine Loan | Minimum
Schedule of Borrowings [Line Items]
Basis spread on variable rate (in percent)				5.25%
Prime Rate | UNI credit facility | Minimum | Revolving credit facility
Schedule of Borrowings [Line Items]
Basis spread on variable rate (in percent)					1.00%
Prime Rate | UNI credit facility | Maximum | Revolving credit facility
Schedule of Borrowings [Line Items]
Basis spread on variable rate (in percent)					4.25%
London Interbank Offered Rate (LIBOR) | ULT Warehouse Credit Facility | Minimum | Revolving credit facility
Schedule of Borrowings [Line Items]
Basis spread on variable rate (in percent)						1.90%
London Interbank Offered Rate (LIBOR) | ULT Warehouse Credit Facility | Maximum | Revolving credit facility
Schedule of Borrowings [Line Items]
Basis spread on variable rate (in percent)						400.00%
Weighted-Average Cost Of Commercial Paper Notes Issued By The Lender | UAWT Warehouse Credit Facility | Minimum | Revolving credit facility
Schedule of Borrowings [Line Items]
Basis spread on variable rate (in percent)		1.80%
Weighted-Average Cost Of Commercial Paper Notes Issued By The Lender | UAWT Warehouse Credit Facility | Maximum | Revolving credit facility
Schedule of Borrowings [Line Items]
Basis spread on variable rate (in percent)		3.50%