CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue:
Revenue	$ 125,750	$ 145,537	$ 237,357	$ 278,905
Expenses:
Cost of sales	2,958	3,012	5,537	5,561
Research, development and patent	139,306	122,264	279,107	239,214
Selling, general and administrative	56,455	72,015	117,653	147,009
Total operating expenses	198,719	197,291	402,297	391,784
Loss from operations	(72,969)	(51,754)	(164,940)	(112,879)
Other income (expense):
Investment income	2,734	9,243	7,364	19,459
Interest expense	(2,357)	(2,441)	(4,771)	(4,648)
Gain on investments	860	9,625	873	9,887
Loss on early retirement of debt	(8,627)	0	(8,627)	0
Other expenses	(189)	(149)	(186)	(249)
Loss before income tax (expense) benefit	(80,548)	(35,476)	(170,287)	(88,430)
Income tax (expense) benefit	(327)	(2,084)	(457)	988
Net loss	(80,875)	(37,560)	(170,744)	(87,442)
Net loss attributable to noncontrolling interest in Akcea Therapeutics, Inc.	0	11,924	0	22,178
Net loss attributable to Ionis Pharmaceuticals, Inc. common stockholders	$ (80,875)	$ (25,636)	$ (170,744)	$ (65,264)
Basic net loss per share (in dollars per share)	$ (0.57)	$ (0.18)	$ (1.21)	$ (0.47)
Diluted net loss per share (in dollars per share)	$ (0.57)	$ (0.18)	$ (1.21)	$ (0.47)
Shares used in computing basic net loss per share (in shares)	140,962	139,352	140,866	139,391
Shares used in computing diluted net loss per share (in shares)	140,962	139,352	140,866	139,391
Commercial Revenue [Member]
Revenue:
Revenue	$ 85,861	$ 89,734	$ 170,309	$ 173,696
SPINRAZA Royalties [Member]
Revenue:
Revenue	72,168	71,746	132,154	137,754
TEGSEDI and WAYLIVRA Revenue, Net [Member]
Revenue:
Revenue	11,544	16,364	31,382	31,523
Licensing and Other Royalty Revenue [Member]
Revenue:
Revenue	2,149	1,624	6,773	4,419
Research and Development Revenue Under Collaborative Agreements [Member]
Revenue:
Revenue	$ 39,889	$ 55,803	$ 67,048	$ 105,209