CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) [Abstract]
Net income (loss)	$ (10,012)	$ (56,570)	$ 80,873	$ (67,381)
Unrealized gains (losses) on debt securities, net of tax	3,452	563	7,775	(967)
Currency translation adjustment	(96)	37	(11)	92
Comprehensive income (loss)	(6,656)	(55,970)	88,637	(68,256)
Comprehensive loss attributable to noncontrolling interests	(9,136)	(14,663)	(2,696)	(24,062)
Comprehensive income (loss) attributable to Ionis Pharmaceuticals, Inc. stockholders	$ 2,480	$ (41,307)	$ 91,333	$ (44,194)