CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS [Abstract]
Net loss	$ (80,875)	$ (37,560)	$ (170,744)	$ (87,442)
Unrealized gains (losses) on debt securities, net of tax	(1,697)	11,204	(4,703)	9,251
Currency translation adjustment	104	74	(22)	82
Comprehensive loss	(82,468)	(26,282)	(175,469)	(78,109)
Comprehensive loss attributable to noncontrolling interest in Akcea Therapeutics, Inc.	0	(11,441)	0	(21,695)
Comprehensive loss attributable to Ionis Pharmaceuticals, Inc. common stockholders	$ (82,468)	$ (14,841)	$ (175,469)	$ (56,414)