CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) [Abstract]
Net income (loss)	$ (486,766)	$ 303,262	$ 214,985
Unrealized gains (losses) on investments, net of tax	3,729	6,633	(280)
Currency translation adjustment	617	93	23
Adjustments to other comprehensive loss from purchase of noncontrolling interest of Akcea Therapeutics, Inc.	(127)	0	0
Comprehensive income (loss)	(482,547)	309,988	214,728
Comprehensive income (loss) attributable to noncontrolling interest in Akcea Therapeutics, Inc.	(35,480)	9,118	(58,781)
Comprehensive income (loss) attributable to Ionis Pharmaceuticals, Inc. common stockholders	$ (447,067)	$ 300,870	$ 273,509