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
Temporary equity, Beginning Balance at Dec. 31, 2018					$ 129,870
Temporary equity, Beginning Balance, Shares at Dec. 31, 2018					207,164,404
Temporary equity, Ending Balance at Mar. 31, 2019					$ 129,870
Temporary equity, Ending Balance, Shares at Mar. 31, 2019					207,164,404
Beginning Balance at Dec. 31, 2018	$ (84,774)	$ 1	$ 2,389	$ (87,164)
Beginning Balance, Shares at Dec. 31, 2018		6,355,377
Vesting of share-based awards		223,072
Stock-based compensation expense	255		255
Net loss	(10,771)			(10,771)
Ending Balance at Mar. 31, 2019	(95,290)	$ 1	2,644	(97,935)
Ending Balance, Shares at Mar. 31, 2019		6,578,449
Temporary equity, Beginning Balance at Dec. 31, 2018					$ 129,870
Temporary equity, Beginning Balance, Shares at Dec. 31, 2018					207,164,404
Temporary equity, Ending Balance at Jun. 30, 2019					$ 129,870
Temporary equity, Ending Balance, Shares at Jun. 30, 2019					207,164,404
Beginning Balance at Dec. 31, 2018	(84,774)	$ 1	2,389	(87,164)
Beginning Balance, Shares at Dec. 31, 2018		6,355,377
Net loss	(19,580)
Ending Balance at Jun. 30, 2019	(103,914)	$ 1	2,829	(106,744)
Ending Balance, Shares at Jun. 30, 2019		6,683,576
Temporary equity, Beginning Balance at Mar. 31, 2019					$ 129,870
Temporary equity, Beginning Balance, Shares at Mar. 31, 2019					207,164,404
Temporary equity, Ending Balance at Jun. 30, 2019					$ 129,870
Temporary equity, Ending Balance, Shares at Jun. 30, 2019					207,164,404
Beginning Balance at Mar. 31, 2019	(95,290)	$ 1	2,644	(97,935)
Beginning Balance, Shares at Mar. 31, 2019		6,578,449
Vesting of share-based awards		105,127
Stock-based compensation expense	185		185
Net loss	(8,809)			(8,809)
Ending Balance at Jun. 30, 2019	(103,914)	$ 1	2,829	(106,744)
Ending Balance, Shares at Jun. 30, 2019		6,683,576
Temporary equity, Beginning Balance at Dec. 31, 2019	$ 129,870				$ 129,870
Temporary equity, Beginning Balance, Shares at Dec. 31, 2019	207,164,404				207,164,404
Temporary equity, Ending Balance at Mar. 31, 2020					$ 129,870
Temporary equity, Ending Balance, Shares at Mar. 31, 2020					207,164,404
Beginning Balance at Dec. 31, 2019	$ (118,603)	$ 1	3,304	(121,908)
Beginning Balance, Shares at Dec. 31, 2019		7,034,047
Vesting of share-based awards		88,080
Stock-based compensation expense	247		247
Net loss	(6,402)			(6,402)
Ending Balance at Mar. 31, 2020	(124,758)	$ 1	3,551	(128,310)
Ending Balance, Shares at Mar. 31, 2020		7,122,127
Temporary equity, Beginning Balance at Dec. 31, 2019	$ 129,870				$ 129,870
Temporary equity, Beginning Balance, Shares at Dec. 31, 2019	207,164,404				207,164,404
Temporary equity, Ending Balance, Shares at Jun. 30, 2020	0				0
Beginning Balance at Dec. 31, 2019	$ (118,603)	$ 1	3,304	(121,908)
Beginning Balance, Shares at Dec. 31, 2019		7,034,047
Conversion of Compass Therapeutics LLC preferred shares into common shares upon consummation of the reverse merger, Shares		30,629,606
Net loss	(11,959)
Ending Balance at Jun. 30, 2020	$ 53,250	$ 5	187,112	(133,867)
Ending Balance, Shares at Jun. 30, 2020		50,896,833
Temporary equity, Beginning Balance at Mar. 31, 2020					$ 129,870
Temporary equity, Beginning Balance, Shares at Mar. 31, 2020					207,164,404
Temporary equity, Conversion of Compass Therapeutics LLC preferred shares into common shares upon consummation of the reverse merger					$ (129,870)
Temporary equity, Conversion of Compass Therapeutics LLC preferred shares into common shares upon consummation of the reverse merger, Shares					(207,164,404)
Temporary equity, Ending Balance, Shares at Jun. 30, 2020	0				0
Beginning Balance at Mar. 31, 2020	$ (124,758)	$ 1	3,551	(128,310)
Beginning Balance, Shares at Mar. 31, 2020		7,122,127
Common shares issued to former shareholders of Olivia Ventures Inc., Shares		1,000,000
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		30,629,606
Common shares issued in private placement, net of issuance costs of $6,902	53,581	$ 1	53,580
Common shares issued in private placement, net of issuance costs of $6,902, Shares		12,096,442
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		(13,641)
Vesting of share-based awards		62,298
Stock-based compensation expense	183		183
Net loss	(5,557)			(5,557)
Ending Balance at Jun. 30, 2020	$ 53,250	$ 5	$ 187,112	$ (133,867)
Ending Balance, Shares at Jun. 30, 2020		50,896,833