Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Total	Total Upstart Holdings, Inc. Stockholders’ Equity (Deficit)	Common Stock	Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)	Noncontrolling Interest
Beginning balance (in shares) at Dec. 31, 2018	46,882,877,000
Beginning balance at Dec. 31, 2018	$ 157,923
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of Series D convertible preferred stock, net of issuance costs of $8 (in shares)	444,428,000
Issuance of Series D convertible preferred stock, net of issuance costs of $8	$ 3,992
Issuance of Series B convertible preferred stock upon exercise of convertible preferred stock warrants (in shares)	300,103,000
Issuance of Series B convertible preferred stock upon exercise of convertible preferred stock warrants	$ 1,631
Repurchase and retirement of Series C convertible preferred stock (in shares)	277,831,000
Repurchase and retirement of Series C convertible preferred stock	$ (1,000)
Ending balance (in shares) at Dec. 31, 2019	47,349,577,000
Ending balance at Dec. 31, 2019	$ 162,546
Beginning balance (in shares) at Dec. 31, 2018			12,991,270,000
Beginning balance at Dec. 31, 2018	(54,670)	$ (66,671)	$ 1	$ 8,406	$ (75,078)	$ 12,001
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase and retirement of Series C convertible preferred stock	339	339			339
Exercise of common stock warrants (in shares)			1,297,884
Issuance of common stock upon exercise of stock options (in shares)			272,244
Issuance of common stock upon exercise of stock options	278	278	$ 1	277
Stock-based compensation expense	3,806	3,806		3,806
Return of capital to interests in consolidated VIEs	(4,960)					(4,960)
Deconsolidation of interests in consolidated VIEs	(1,461)					(1,461)
Net income	(5,020)	(466)			(466)	(4,554)
Ending balance (in shares) at Dec. 31, 2019			14,561,398,000
Ending balance at Dec. 31, 2019	$ (61,688)	(62,714)	$ 2	12,489	(75,205)	1,026
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)	(47,349,577,000)
Conversion of convertible preferred stock to common stock upon initial public offering	$ (162,546)
Ending balance (in shares) at Dec. 31, 2020	0
Ending balance at Dec. 31, 2020	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock warrants (in shares)			235,625,000
Exercise of common stock warrants	2,971	2,971		2,971
Issuance of common stock upon exercise of stock options (in shares)			1,284,468,000
Issuance of common stock upon exercise of stock options	2,362	2,362		2,362
Stock-based compensation expense	12,005	12,005		12,005
Return of capital to interests in consolidated VIEs	(622)					(622)
Net income	5,579	5,983			5,983	(404)
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)			47,349,577,000
Conversion of convertible preferred stock to common stock upon initial public offering	162,546	162,546	$ 4	162,542
Issuance of common stock net of underwriting discounts, commissions, and offering costs (in shares)			9,000,000,000
Issuance of common stock net of underwriting discounts, commissions, and offering costs	159,488	159,488	$ 1	159,487
Issuance of common stock in connection with an incentive agreement (in shares)			282,750,000
Issuance of common stock in connection with an incentive agreement	1,696	1,696		1,696
Exercise of convertible preferred stock warrant into preferred stock and issuance of common stock upon initial public offering (in shares)			600,208,000
Exercise of convertible preferred stock warrant into preferred stock and issuance of common stock upon initial public offering	12,183	12,183		12,183
Reclass of warrant liability upon termination of repurchase obligation	2,945	2,945		2,945
Incentive share expense	$ 787	787		787
Ending balance (in shares) at Dec. 31, 2020	73,314,026		73,314,026,000
Ending balance at Dec. 31, 2020	$ 300,252	300,252	$ 7	369,467	(69,222)	0
Ending balance (in shares) at Dec. 31, 2021	0
Ending balance at Dec. 31, 2021	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock warrants (in shares)			72,407,000
Issuance of common stock upon exercise of stock options (in shares)	7,047,722,000		7,047,722,000
Issuance of common stock upon exercise of stock options	$ 14,736	14,736		14,736
Stock-based compensation expense	76,327	76,327		76,327
Net income	135,443	135,443			135,443
Issuance of common stock net of underwriting discounts, commissions, and offering costs (in shares)			2,300,000,000
Issuance of common stock net of underwriting discounts, commissions, and offering costs	263,931	263,931	$ 1	263,930
Issuance of common stock upon settlement of restricted stock units (in shares)			32,775,000
Shares withheld related to net share settlement of restricted stock units (in shares)			(1,730,000)
Shares withheld related to net share settlement of restricted stock units	$ (236)	(236)		(236)
Issuance of common stock in connection with an acquisition (in shares)	650,740,000
Issuance of common stock in connection with acquisition	$ 71,003
Issuance of common stock under employee stock purchase plan (in shares)			243,725,000
Issuance of common stock under employee stock purchase plan	4,145	4,145		4,145
Purchase of capped calls	$ (58,523)	(58,523)		(58,523)
Ending balance (in shares) at Dec. 31, 2021	83,659,665		83,659,665,000
Ending balance at Dec. 31, 2021	$ 807,078	$ 807,078	$ 8	$ 740,849	$ 66,221	$ 0