Income per Share - Reconciliation of Basic and Diluted Income Per Share Computations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Net income attributable to Fulgent	$ (23,832)	$ 1,719	$ 11,537	$ 153,979	$ 104,339	$ 122,522	$ 79,812	$ 200,691	$ 143,403	$ 507,364	$ 214,310
Weighted-average common shares - outstanding, basic									30,097	29,408	22,694
Weighted-average common shares - outstanding, diluted									30,964	30,976	24,056
Net income per common share, basic	$ (0.80)	$ 0.06	$ 0.38	$ 5.09	$ 3.48	$ 4.13	$ 2.74	$ 6.96	$ 4.76	$ 17.25	$ 9.44
Net income per common share, diluted	$ (0.80)	$ 0.06	$ 0.37	$ 4.93	$ 3.34	$ 3.93	$ 2.59	$ 6.52	$ 4.63	$ 16.38	$ 8.91