Warrants - Narrative (Details)		1 Months Ended	2 Months Ended	3 Months Ended	9 Months Ended
	Aug. 05, 2019 USD ($) $ / shares shares	Aug. 31, 2020 USD ($) $ / shares shares	May 31, 2020 $ / shares shares	Sep. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Mar. 11, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 21, 2020 shares	Apr. 03, 2020 USD ($) $ / shares shares	Nov. 27, 2018 USD ($) $ / shares shares
Class of Warrant or Right [Line Items]
Warrant, fair value				$ 10,979,000	$ 10,979,000			$ 49,293,000
Warrants, loss (gain) from fair value adjustment					406,000	$ 6,097,000
Warrants outstanding (in shares) | shares							15,999,996
CLA | Conversion of Warrant to Ouster Common Stock
Class of Warrant or Right [Line Items]
Warrant, conversion ratio									1
OTI | Series B Redeemable Convertible Preferred Stock
Class of Warrant or Right [Line Items]
Issuance of redeemable convertible preferred stock (in shares) | shares			62,505,102
Preferred stock issued (in dollars per share) | $ / shares			$ 0.3323
Series A Redeemable Convertible Preferred Stock Warrants
Class of Warrant or Right [Line Items]
Warrants issued, number of preferred stock callable (in shares) | shares	53,023										35,348
Warrants issued, exercise price (in dollars per share) | $ / shares											$ 11.3518
Warrants, loss (gain) from fair value adjustment	$ 100,000
Series A Redeemable Convertible Preferred Stock Warrants | OTI
Class of Warrant or Right [Line Items]
Warrants issued, number of preferred stock callable (in shares) | shares	53,023										35,348
Warrants issued, exercise price (in dollars per share) | $ / shares	$ 11.3518										$ 11.3518
Warrant, fair value	$ 100,000										$ 100,000
Series A Redeemable Convertible Preferred Stock Warrants | Other Income (Expense), Net
Class of Warrant or Right [Line Items]
Warrants, loss (gain) from fair value adjustment				600,000	600,000	$ (200,000)
Series B Redeemable Convertible Preferred Stock Warrants | OTI
Class of Warrant or Right [Line Items]
Warrants issued, number of preferred stock callable (in shares) | shares										4,513,993
Warrants issued, exercise price (in dollars per share) | $ / shares										$ 0.3323
Warrant, fair value										$ 700,000
Series B Redeemable Convertible Preferred Stock Warrants | Other Income (Expense), Net | OTI
Class of Warrant or Right [Line Items]
Warrants, loss (gain) from fair value adjustment					8,300,000
Series B Redeemable Convertible Preferred Stock Warrants | Maximum | OTI
Class of Warrant or Right [Line Items]
Warrant, expiration period										10 years
Redeemable Convertible Preferred Stock Tranche Right | OTI
Class of Warrant or Right [Line Items]
Warrants issued, exercise price (in dollars per share) | $ / shares			$ 0.3323
Private Placement Warrants | Sponsor
Class of Warrant or Right [Line Items]
Warrants issued, number of preferred stock callable (in shares) | shares		6,000,000
Warrants issued, exercise price (in dollars per share) | $ / shares		$ 11.50
Warrant, fair value		$ 19,400,000
Warrant, expiration period		5 years
Sale of warrants, price (in dollars per share) | $ / shares		$ 1.00
Warrant, aggregated purchase price		$ 6,000,000
Warrant, exercisable, threshold period		12 months
Number of ordinary shares called by each warrant (in shares) | shares		1
Private Placement Warrants | Sponsor | Conversion of Warrant to Ouster Common Stock
Class of Warrant or Right [Line Items]
Warrant, conversion ratio							1
Private Placement Warrants | CLA
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares) | shares									6,000,000
Private Placement Warrants | Other Income (Expense), Net | Sponsor
Class of Warrant or Right [Line Items]
Warrants, loss (gain) from fair value adjustment				$ 14,500,000	$ 8,400,000
Public Warrants
Class of Warrant or Right [Line Items]
Sale of warrants, price (in dollars per share) | $ / shares		$ 0.01
Exercise of warrant, threshold common stock price (in dollars per share) | $ / shares		$ 18.00
Exercise of warrant, threshold trading days		20 days
Exercise of warrant, threshold trading-day period		30 days
Public Warrants | CLA
Class of Warrant or Right [Line Items]
Warrants issued, number of preferred stock callable (in shares) | shares		20,000,000
Warrants issued, exercise price (in dollars per share) | $ / shares		$ 11.50
Warrant, fair value							$ 17,900,000
Warrant, expiration period		5 years
Warrant, exercisable, threshold period		12 months
Warrant, conversion ratio		1
Warrants outstanding (in shares) | shares							9,999,996