Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands		Dec. 31, 2021	Dec. 31, 2020
Variable Interest Entity or Potential VIE, Information Unavailability, Disclosures [Abstract]
Cash		$ 986,608	$ 250,819
Restricted cash		204,633	60,514
Other assets (includes $6,831 and $18,388 at fair value as of December 31, 2020 and 2021, respectively)		121,104	40,046
Total assets	[1]	1,820,455	477,255
Accounts payable		6,563	13,775
Borrowings		695,432	62,626
Accrued expenses and other liabilities (includes $9,530 and $13,095 at fair value as of December 31, 2020 and 2021, respectively)		103,418	35,669
Total liabilities	[1]	1,013,377	177,003
Other assets at fair value		18,388	6,831
Accrued expenses and other liabilities at fair value		$ 13,095	$ 9,530
Common stock, par value (in dollars per share)		$ 0.0001	$ 0.0001
Common stock, authorized (in shares)		700,000,000	700,000,000
Common stock, issued (in shares)		83,659,665	73,314,026
Common stock, outstanding (in shares)		83,659,665	73,314,026
Loans (at fair value)
Variable Interest Entity or Potential VIE, Information Unavailability, Disclosures [Abstract]
Loans, notes receivables, and residual certificates		$ 252,477	$ 78,460
Notes receivable and residual certificates (at fair value)
Variable Interest Entity or Potential VIE, Information Unavailability, Disclosures [Abstract]
Loans, notes receivables, and residual certificates		8,288	19,074
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity or Potential VIE, Information Unavailability, Disclosures [Abstract]
Cash		7,700	0
Restricted cash		79,561	12,371
Other assets (includes $6,831 and $18,388 at fair value as of December 31, 2020 and 2021, respectively)		1,221	29
Total assets		342,025	104,992
Accounts payable		0	83
Borrowings		48,536	42,181
Accrued expenses and other liabilities (includes $9,530 and $13,095 at fair value as of December 31, 2020 and 2021, respectively)		778	32
Total liabilities		49,314	42,296
Variable Interest Entity, Primary Beneficiary | Loans (at fair value)
Variable Interest Entity or Potential VIE, Information Unavailability, Disclosures [Abstract]
Loans, notes receivables, and residual certificates		245,972	75,373
Variable Interest Entity, Primary Beneficiary | Notes receivable and residual certificates (at fair value)
Variable Interest Entity or Potential VIE, Information Unavailability, Disclosures [Abstract]
Loans, notes receivables, and residual certificates		$ 7,571	$ 17,219

[1] The following table presents information on assets and liabilities related to variable interest entities (“VIEs”) that are consolidated by Upstart Holdings, Inc. at December 31, 2020 and 2021. The assets in the table below may only be used to settle obligations of consolidated VIEs and are in excess of those obligations. The holders of the beneficial interests do not have recourse to the general credit of Upstart Holdings, Inc. The assets and liabilities in the table below include third-party assets and liabilities of consolidated VIEs and exclude intercompany balances that eliminate in consolidation. December 31,December 31,20202021AssetsCash $— $7,700 Restricted cash12,371 79,561 Loans (at fair value)75,373 245,972 Notes receivable and residual certificates (at fair value)17,219 7,571 Other assets29 1,221 Total assets$104,992 $342,025 LiabilitiesAccounts payable$83 $— Borrowings42,181 48,536 Other liabilities 32 778 Total liabilities$42,296 $49,314