Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Aug. 02, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	AKCEA THERAPEUTICS, INC.
Entity Central Index Key	0001662524
Document Type	10-Q
Document Period End Date	Jun. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		66,541,629
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q2