CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) [Abstract]
Net income (loss)	$ 90,884	$ (10,812)
Unrealized gains (losses) on debt securities, net of tax	4,324	(1,530)
Currency translation adjustment	84	55
Comprehensive income (loss)	95,292	(12,287)
Comprehensive (income) loss attributable to noncontrolling interests	6,442	(9,399)
Comprehensive income (loss) attributable to Ionis Pharmaceuticals, Inc. stockholders	$ 88,850	$ (2,888)