Sutro Biopharma, Inc. Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity (Deficit) - Schedule of Warrants Related to Redeemable Convertible Preferred Stock Outstanding and Exercisable Estimated Fair Value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Class Of Warrant Or Right [Line Items]
Shares		3,331,972
Estimated fair value	$ 0	$ 1,708
Series B Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Expiration date	2018-06	2018-06
Shares		170,030
Estimated fair value	$ 0	$ 116
Series C Preferred Stock
Class Of Warrant Or Right [Line Items]
Expiration date	2018-09
Shares		2,479,712
Estimated fair value	$ 0	$ 1,263
Series C Preferred Stock \| Minimum
Class Of Warrant Or Right [Line Items]
Expiration date	2021-11
Series C Preferred Stock \| Maximum
Class Of Warrant Or Right [Line Items]
Expiration date	2022-06
Series D-2 Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Expiration date	2018-09	2018-09
Shares		682,230
Estimated fair value	$ 0	$ 329
Series E Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Expiration date	2018-09	2018-09
Shares		0
Estimated fair value	$ 0