Condensed Consolidated Statements of Changes in Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Convertible Preferred Stock
Beginning Balance at Dec. 31, 2019	$ (118,603)	$ 1	$ 3,304	$ (121,908)
Temporary equity, Beginning Balance, Shares at Dec. 31, 2019					207,164,000
Temporary equity, Beginning Balance at Dec. 31, 2019					$ 129,870
Beginning Balance, Shares at Dec. 31, 2019		7,034,000
Vesting of share-based awards		88,000
Stock-based compensation	247		247
Net loss	6,402			6,402
Ending Balance at Mar. 31, 2020	(124,758)	$ 1	3,551	(128,310)
Temporary equity, Ending Balance, Shares at Mar. 31, 2020					207,164,000
Temporary equity, Ending Balance at Mar. 31, 2020					$ 129,870
Ending Balance, Shares at Mar. 31, 2020		7,122,000
Vesting of share-based awards		62,000
Stock-based compensation	183		183
Common shares issued in private placement, net of issuance costs of $6,902, Shares		12,097,000
Common shares issued in private placement, net of issuance costs of $6,902	53,581	$ 1	53,580
Common shares issued for acquisitions, Shares		1,000,000
Temporary equity, Conversion of Compass Therapeutics LLC preferred shares into common shares upon consummation of the reverse merger, Shares					(207,164,000)
Temporary equity, Conversion of Compass Therapeutics LLC preferred shares into common shares upon consummation of the reverse merger					$ (129,870)
Conversion of compass Therapeutics LLC preferred shares into common shares upon consummation of the reverse merger	129,870	$ 3	129,867
Conversion of compass Therapeutics LLC preferred shares into common shares upon consummation of the reverse merger, Shares		30,630,000
Payment to non-participating Compass Therapeutics LLC members upon consummation of Merger	(69)		(69)
Payment to non-participating Compass Therapeutics LLC members upon consummation of Merger, Shares		(14,000)
Net loss	5,557			5,557
Ending Balance at Jun. 30, 2020	53,250	$ 5	187,112	(133,867)
Temporary equity, Ending Balance, Shares at Jun. 30, 2020					0
Temporary equity, Ending Balance at Jun. 30, 2020					$ 0
Ending Balance, Shares at Jun. 30, 2020		50,897,000
Beginning Balance at Dec. 31, 2020	39,945	$ 5	191,348	(151,408)
Temporary equity, Beginning Balance, Shares at Dec. 31, 2020					0
Temporary equity, Beginning Balance at Dec. 31, 2020					$ 0
Beginning Balance, Shares at Dec. 31, 2020		51,221,000
Vesting of share-based awards		92,000
Stock-based compensation	948		948
Net loss	7,422			7,422
Ending Balance at Mar. 31, 2021	33,471	$ 5	192,296	(158,830)
Temporary equity, Ending Balance, Shares at Mar. 31, 2021					0
Temporary equity, Ending Balance at Mar. 31, 2021					$ 0
Ending Balance, Shares at Mar. 31, 2021		51,313,000
Vesting of share-based awards		88,000
Stock-based compensation	908		908
Common shares issued for acquisitions	50,300	$ 1	50,299
Common shares issued for acquisitions, Shares		10,265,000
Net loss	(55,804)			(55,804)
Ending Balance at Jun. 30, 2021	$ 28,875	$ 6	$ 243,503	$ (214,634)
Temporary equity, Ending Balance, Shares at Jun. 30, 2021					0
Temporary equity, Ending Balance at Jun. 30, 2021					$ 0
Ending Balance, Shares at Jun. 30, 2021		61,666,000