Net Loss Per Share - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Numerator:
Net loss attributable to Forge Global Holdings, Inc., basic	$ (16,198)	$ (5,074)	$ (85,741)	$ (12,139)
Less: Decrease in fair value of Junior Preferred warrants	(3,937)	0	(3,897)	0
Net loss attributable to common stockholders, diluted	$ (20,135)	$ (5,074)	$ (89,638)	$ (12,139)
Denominator:
Weighted-average number of shares used to compute net loss per share attributable to common stockholders, basic (in shares)	169,838,778	51,450,791	134,683,950	55,147,414
Dilutive effect of common share equivalents (in shares)	370,478	0	1,276,662	0
Dilutive effect of common share equivalents (in shares)	170,209,256	51,450,791	135,960,612	55,147,414
Net loss per share attributable to Forge Global Holdings, Inc. common stockholders:
Basic (in dollars per share)	$ (0.10)	$ (0.10)	$ (0.64)	$ (0.22)
Diluted (in dollars per share)	$ (0.12)	$ (0.10)	$ (0.66)	$ (0.22)