Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Aug. 01, 2019
Document And Entity Information [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, 2019  
Amendment Flag false  
Trading Symbol AKCA  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Common Stock Shares Outstanding   93,032,386
Document Fiscal Year Focus 2019  
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 MA  
Document Quarterly Report true  
Document Transition Report false