CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue:
Revenue	$ 729,264	$ 1,122,599	$ 599,674
Expenses:
Cost of products sold	11,947	4,384	1,820
Research, development and patent	535,077	465,688	414,604
Selling, general and administrative	354,322	286,644	244,622
Total operating expenses	901,346	756,716	661,046
Income (loss) from operations	(172,082)	365,883	(61,372)
Other income (expense):
Investment income	30,562	52,013	30,397
Interest expense	(44,990)	(48,768)	(44,789)
Gain (loss) on investments	16,540	192	(210)
Loss on early retirement of debt	0	(21,865)	0
Other expenses	(62)	(686)	(182)
Income (loss) before income tax benefit (expense)	(170,032)	346,769	(76,156)
Income tax benefit (expense)	(316,734)	(43,507)	291,141
Net income (loss)	(486,766)	303,262	214,985
Net (income) loss attributable to noncontrolling interest in Akcea Therapeutics, Inc.	35,480	(9,116)	58,756
Net income (loss) attributable to Ionis Pharmaceuticals, Inc. common stockholders	$ (451,286)	$ 294,146	$ 273,741
Basic net income (loss) per share (in dollars per share)	$ (3.23)	$ 2.12	$ 2.09
Shares used in computing basic net income (loss) per share (in shares)	139,612	139,998	132,320
Diluted net income (loss) per share (in dollars per share)	$ (3.23)	$ 2.08	$ 2.07
Shares used in computing diluted net income (loss) per share (in shares)	139,612	142,872	134,056
Commercial Revenue [Member]
Revenue:
Revenue	$ 364,699	$ 352,450	$ 254,922
SPINRAZA Royalties [Member]
Revenue:
Revenue	286,583	292,992	237,930
Product Sales, Net [Member]
Revenue:
Revenue	69,999	42,253	2,237
Licensing and Other Royalty Revenue [Member]
Revenue:
Revenue	8,117	17,205	14,755
Research and Development Revenue Under Collaborative Agreements [Member]
Revenue:
Revenue	$ 364,565	$ 770,149	$ 344,752