Condensed Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Equity Distribution Agreement	2020 Equity Distribution Agreement	Cumulative Effect, Period of Adoption, Adjustment	Stockholders' Equity	Stockholders' Equity Equity Distribution Agreement	Stockholders' Equity 2020 Equity Distribution Agreement	Additional Paid-In Capital	Additional Paid-In Capital Equity Distribution Agreement	Additional Paid-In Capital 2020 Equity Distribution Agreement	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Accumulated Deficit)	Retained Earnings (Accumulated Deficit) Cumulative Effect, Period of Adoption, Adjustment	Fulgent Stockholders' Equity	Fulgent Stockholders' Equity Cumulative Effect, Period of Adoption, Adjustment	Noncontrolling Interest
Beginning Balance at Dec. 31, 2019	$ 82,777				$ 2			$ 146,058			$ 146	$ (63,429)
Beginning Balance, Shares at Dec. 31, 2019					21,483
Equity-based compensation	924							924
Exercise of common stock options	12							12
Exercise of common stock options, Shares					33
Restricted stock awards, Shares					159
Common stock withholding for employee tax obligations	(46)							(46)
Common stock withholding for employee tax obligations, Shares					(3)
Other comprehensive gain (loss)	(339)										(339)
Net income (loss)	(1,956)											(1,956)
Ending Balance at Mar. 31, 2020	81,372				$ 2			146,948			(193)	(65,385)
Ending Balance, Shares at Mar. 31, 2020					21,672
Beginning Balance at Dec. 31, 2019	82,777				$ 2			146,058			146	(63,429)
Beginning Balance, Shares at Dec. 31, 2019					21,483
Net income (loss)	48,003
Ending Balance at Sep. 30, 2020	186,955				$ 2			201,772			607	(15,426)
Ending Balance, Shares at Sep. 30, 2020					23,307
Beginning Balance at Mar. 31, 2020	81,372				$ 2			146,948			(193)	(65,385)
Beginning Balance, Shares at Mar. 31, 2020					21,672
Equity-based compensation	1,080							1,080
Exercise of common stock options	28							28
Exercise of common stock options, Shares					11
Restricted stock awards, Shares					127
Other comprehensive gain (loss)	1,242										1,242
Net income (loss)	3,321											3,321
Ending Balance at Jun. 30, 2020	87,043				$ 2			148,056			1,049	(62,064)
Ending Balance, Shares at Jun. 30, 2020					21,810
Equity-based compensation	3,150							3,150
Exercise of common stock options	62							62
Exercise of common stock options, Shares					6
Restricted stock awards, Shares					183
Issuance of common stock		$ 42,655	$ 7,849						$ 42,655	$ 7,849
Issuance of common stock, Shares						1,108	200
Other comprehensive gain (loss)	(442)										(442)
Net income (loss)	46,638											46,638
Ending Balance at Sep. 30, 2020	186,955				$ 2			201,772			607	(15,426)
Ending Balance, Shares at Sep. 30, 2020					23,307
Beginning Balance at Dec. 31, 2020	$ 569,387			$ (887)	$ 3			418,065			438	150,881	$ (887)	$ 569,387	$ (887)
Beginning Balance, Shares at Dec. 31, 2020	28,178				28,178
Equity-based compensation	$ 2,962							2,962						2,962
Exercise of common stock options	44							44						44
Exercise of common stock options, Shares					45
Restricted stock awards, Shares					187
Common stock withholding for employee tax obligations	(513)							(513)						(513)
Common stock withholding for employee tax obligations, Shares					(4)
Issuance of common stock	30,297							30,297						30,297
Issuance of common stock, Shares					583
Other comprehensive gain (loss)	(654)										(654)			(654)
Cumulative tax effect of accounting change	239											239		239
Net income (loss)	200,691											200,691		200,691
Ending Balance at Mar. 31, 2021	801,566				$ 3			450,855			(216)	350,924		801,566
Ending Balance, Shares at Mar. 31, 2021					28,989
Beginning Balance at Dec. 31, 2020	$ 569,387			$ (887)	$ 3			418,065			438	150,881	$ (887)	569,387	$ (887)
Beginning Balance, Shares at Dec. 31, 2020	28,178				28,178
Net income (loss)	$ 402,562
Ending Balance at Sep. 30, 2021	$ 1,044,453				$ 3			483,731			(212)	553,258		1,036,780		$ 7,673
Ending Balance, Shares at Sep. 30, 2021	29,829				29,829
Beginning Balance at Mar. 31, 2021	$ 801,566				$ 3			450,855			(216)	350,924		801,566
Beginning Balance, Shares at Mar. 31, 2021					28,989
Equity-based compensation	3,526							3,526						3,526
Exercise of common stock options	24							24						24
Exercise of common stock options, Shares					4
Restricted stock awards, Shares					143
Common stock withholding for employee tax obligations	(39)							(39)						(39)
Common stock withholding for employee tax obligations, Shares					(1)
Issuance of common stock	27,889							27,889						27,889
Issuance of common stock, Shares					378
Noncontrolling interest assumed related to acquisitions	8,151															8,151
Other comprehensive gain (loss)	(39)										(49)			(49)		10
Net income (loss)	79,647											79,812		79,812		(165)
Ending Balance at Jun. 30, 2021	920,725				$ 3			482,255			(265)	430,736		912,729		7,996
Ending Balance, Shares at Jun. 30, 2021					29,513
Equity-based compensation	4,374							4,374						4,374
Exercise of common stock options	17							17						17
Exercise of common stock options, Shares					25
Restricted stock awards, Shares					320
Common stock withholding for employee tax obligations	(2,915)							(2,915)						(2,915)
Common stock withholding for employee tax obligations, Shares					(29)
Other comprehensive gain (loss)	28										53			53		(25)
Net income (loss)	122,224											122,522		122,522		(298)
Ending Balance at Sep. 30, 2021	$ 1,044,453				$ 3			$ 483,731			$ (212)	$ 553,258		$ 1,036,780		$ 7,673
Ending Balance, Shares at Sep. 30, 2021	29,829				29,829