CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) [Abstract]
Net income (loss)	$ (56,573)	$ (3,085)	$ (67,381)	$ 5,878
Unrealized gains (losses) on debt securities, net of tax	563	130	(967)	396
Reclassification adjustment for realized gains included in net income (loss)	0	0	0	(374)
Currency translation adjustment	37	(42)	92	(36)
Comprehensive income (loss)	(55,973)	(2,997)	(68,256)	5,864
Comprehensive loss attributable to noncontrolling interests	16,237	0	25,659	0
Comprehensive income (loss) attributable to Ionis Pharmaceuticals, Inc. stockholders	$ (39,736)	$ (2,997)	$ (42,597)	$ 5,864