CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS [Abstract]
Net loss	$ (82,466)	$ (36,614)	$ (253,210)	$ (124,056)
Unrealized gains (losses) on debt securities, net of tax	(1,618)	(3,448)	(6,321)	5,803
Currency translation adjustment	(23)	275	(45)	357
Comprehensive loss	(84,107)	(39,787)	(259,576)	(117,896)
Comprehensive loss attributable to noncontrolling interest in Akcea Therapeutics, Inc.	0	(12,188)	0	(33,883)
Comprehensive loss attributable to Ionis Pharmaceuticals, Inc. common stockholders	$ (84,107)	$ (27,599)	$ (259,576)	$ (84,013)