Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 29, 2020
Cover [Abstract]
Entity Registrant Name	Akcea Therapeutics, Inc.
Entity Central Index Key	0001662524
Entity Current Reporting Status	Yes
Document Type	10-Q
Document Period End Date	Jun. 30, 2020
Amendment Flag	false
Trading Symbol	AKCA
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock Shares Outstanding		101,598,619
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Address, Address Line One	22 Boston Wharf Road
Entity Address, Address Line Two	9th Floor
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02210
City Area Code	617
Local Phone Number	207-0202
Entity File Number	001-38137
Entity Tax Identification Number	47-2608175
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false