CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Revenue	$ 1,122,599	$ 599,674	$ 514,179
Expenses:
Cost of products sold	4,384	1,820	0
Research, development and patent	465,688	414,604	374,644
Selling, general and administrative	286,644	244,622	108,488
Total operating expenses	756,716	661,046	483,132
Income (loss) from operations	365,883	(61,372)	31,047
Other income (expense):
Investment income	52,205	30,187	8,179
Interest expense	(48,768)	(44,789)	(44,752)
Loss on extinguishment of financing liability for leased facility	0	0	(7,689)
Loss on early retirement of debt	(21,865)	0	0
Other expenses	(686)	(182)	(3,548)
Income (loss) before income tax benefit (expense)	346,769	(76,156)	(16,763)
Income tax benefit (expense)	(43,507)	291,141	5,980
Net income (loss)	303,262	214,985	(10,783)
Net (income) loss attributable to noncontrolling interest in Akcea Therapeutics, Inc.	(9,116)	58,756	11,129
Net income attributable to Ionis Pharmaceuticals, Inc. common stockholders	$ 294,146	$ 273,741	$ 346
Basic net income per share (in dollars per share)	$ 2.12	$ 2.09	$ 0.15
Shares used in computing basic net income per share (in shares)	139,998	132,320	124,016
Diluted net income per share (in dollars per share)	$ 2.08	$ 2.07	$ 0.15
Shares used in computing diluted net income per share (in shares)	142,872	134,056	126,098
Commercial Revenue [Member]
Revenue:
Revenue	$ 352,450	$ 254,922	$ 120,014
SPINRAZA Royalties [Member]
Revenue:
Revenue	292,992	237,930	112,540
Product Sales, Net [Member]
Revenue:
Revenue	42,253	2,237	0
Licensing and Other Royalty Revenue [Member]
Revenue:
Revenue	17,205	14,755	7,474
Research and Development Revenue Under Collaborative Agreements [Member]
Revenue:
Revenue	$ 770,149	$ 344,752	$ 394,165