CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue:
Revenue	$ 111,607	$ 133,367
Expenses:
Cost of sales	2,578	2,548
Research, development and patent	139,801	116,952
Selling, general and administrative	61,199	74,994
Total operating expenses	203,578	194,494
Loss from operations	(91,971)	(61,127)
Other income (expense):
Investment income	4,643	10,479
Interest expense	(2,414)	(2,207)
Other income (expenses)	3	(99)
Loss before income tax (expense) benefit	(89,739)	(52,954)
Income tax (expense) benefit	(130)	3,072
Net loss	(89,869)	(49,882)
Net loss attributable to noncontrolling interest in Akcea Therapeutics, Inc.	0	10,254
Net loss attributable to Ionis Pharmaceuticals, Inc. common stockholders	$ (89,869)	$ (39,628)
Basic net loss per share (in dollars per share)	$ (0.64)	$ (0.28)
Diluted net loss per share (in dollars per share)	$ (0.64)	$ (0.28)
Shares used in computing basic net loss per share (in shares)	140,770	139,429
Shares used in computing diluted net loss per share (in shares)	140,770	139,429
Commercial Revenue [Member]
Revenue:
Revenue	$ 84,448	$ 83,961
SPINRAZA Royalties [Member]
Revenue:
Revenue	59,986	66,008
TEGSEDI and WAYLIVRA Revenue, Net [Member]
Revenue:
Revenue	19,838	15,159
Licensing and Other Royalty Revenue [Member]
Revenue:
Revenue	4,624	2,794
Research and Development Revenue Under Collaborative Agreements [Member]
Revenue:
Revenue	$ 27,159	$ 49,406