Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)	Total Upstart Holdings, Inc. Stockholders’ Equity (Deficit)	Noncontrolling Interest
Beginning balance (in shares) at Dec. 31, 2019	47,349,577
Beginning balance at Dec. 31, 2019	$ 162,546
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)	(47,349,577)
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
Beginning balance (in shares) at Dec. 31, 2019		14,561,398
Beginning balance at Dec. 31, 2019	(61,688)	$ 2	$ 12,489	$ (75,205)	$ (62,714)	$ 1,026
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of convertible preferred stock to common stock upon initial public offering (in shares)		47,349,577
Conversion of convertible preferred stock to common stock upon initial public offering	162,546	$ 4	162,542		162,546
Issuance of common stock upon initial public offering, net of underwriting discounts, commissions, and offering costs (in shares)		9,000,000
Issuance of common stock upon initial public offering, net of underwriting discounts, commissions, and offering costs	159,488	$ 1	159,487		159,488
Issuance of common stock upon exercise of stock options (in shares)		1,284,468
Issuance of common stock upon exercise of stock options	2,362		2,362		2,362
Issuance of common stock in connection with an incentive agreement (in shares)		282,750
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
Exercise of convertible preferred stock warrant into preferred stock and issuance of common stock upon initial public offering	12,183		12,183		12,183
Exercise of common stock warrants (in shares)		235,625
Exercise of common stock warrants	2,971		2,971		2,971
Reclass of warrant liability upon termination of repurchase obligation	2,945		2,945		2,945
Stock-based compensation expense	12,005		12,005		12,005
Incentive share expense	787		787		787
Return of capital on interest in consolidated VIEs	(622)					(622)
Net income (loss)	5,579			5,983	5,983	(404)
Ending balance (in shares) at Dec. 31, 2020		73,314,026
Ending balance at Dec. 31, 2020	300,252	$ 7	369,467	(69,222)	300,252	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon initial public offering, net of underwriting discounts, commissions, and offering costs (in shares)		2,300,000
Issuance of common stock upon initial public offering, net of underwriting discounts, commissions, and offering costs	263,931	$ 1	263,930		263,931
Issuance of common stock upon exercise of stock options (in shares)		7,047,722
Issuance of common stock upon exercise of stock options	14,736		14,736		14,736
Exercise of common stock warrants (in shares)		72,407
Stock-based compensation expense	76,327		76,327		76,327
Issuance of common stock upon settlement of restricted stock units (in shares)		32,775
Shares withheld related to net share settlement of restricted stock units (in shares)		(1,730)
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
Issuance of common stock in connection with acquisition	71,003		71,003		71,003
Issuance of common stock under employee stock purchase plan (in shares)		243,725
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)
Net income (loss)	$ 135,443			135,443	135,443
Ending balance (in shares) at Dec. 31, 2021	83,659,665	83,659,665
Ending balance at Dec. 31, 2021	$ 807,078	$ 8	740,849	66,221	807,078	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	2,464,572	2,464,572
Issuance of common stock upon exercise of stock options	$ 12,354	$ 1	12,353		12,354
Stock-based compensation expense	131,905		131,905		131,905
Issuance of common stock upon settlement of restricted stock units (in shares)		866,717
Shares withheld related to net share settlement of restricted stock units (in shares)		(619)
Shares withheld related to net share settlement of restricted stock units	$ (16)		(16)		(16)
Repurchase and retirement of restricted stock (in shares)	(5,900,000)	(10,279)
Issuance of common stock under employee stock purchase plan (in shares)		162,796
Issuance of common stock under employee stock purchase plan	$ 7,662		7,662		7,662
Repurchases of stock (in shares)		(5,883,176)
Repurchases of stock	(177,883)	$ (1)	(177,882)		(177,883)
Net income (loss)	$ (108,665)			(108,665)	(108,665)
Ending balance (in shares) at Dec. 31, 2022	81,259,676	81,259,676
Ending balance at Dec. 31, 2022	$ 672,435	$ 8	$ 714,871	$ (42,444)	$ 672,435	$ 0