CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) [Abstract]
Net income (loss)	$ 18,432	$ (20,365)	$ 99,304	$ (87,747)
Unrealized gains (losses) on debt securities, net of tax	(1,110)	133	6,666	(834)
Currency translation adjustment	(13)	(31)	(25)	61
Comprehensive income (loss)	17,309	(20,263)	105,945	(88,520)
Comprehensive loss attributable to noncontrolling interests	(7,729)	(13,943)	(10,423)	(38,005)
Comprehensive income (loss) attributable to Ionis Pharmaceuticals, Inc. stockholders	$ 25,038	$ (6,320)	$ 116,368	$ (50,515)