Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (42,203)	$ (20,187)
Foreign currency translation adjustment	(1,504)
Change in unrealized gain (loss) on available-for-sale securities	253	(99)
Comprehensive loss	(43,454)	(20,286)
Comprehensive loss attributable to non-controlling interest	(53)
Comprehensive loss attributable to Sangamo Therapeutics, Inc.	$ (43,401)	$ (20,286)