Organization and Significant Accounting Policies, Convertible Debt (Details) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended				12 Months Ended
	Apr. 30, 2021 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2021 USD ($) $ / shares		Dec. 31, 2020 USD ($) Note $ / shares		Dec. 31, 2021 USD ($) $ / shares	Dec. 31, 2020 USD ($) Note $ / shares	Dec. 31, 2019 USD ($) $ / shares	Nov. 30, 2021	Dec. 31, 2018 USD ($)	Dec. 31, 2016 USD ($)	Nov. 30, 2014 USD ($)
Convertible Debt [Abstract]
Number of outstanding convertible notes | Note					2			2
Consolidated Balance Sheet [Abstract]
1 percent convertible senior notes, net			$ 0		$ 308,809		$ 0	$ 308,809
Additional paid-in capital			1,964,167		1,895,519		1,964,167	1,895,519
Accumulated deficit			(1,159,903)		(1,131,306)		(1,159,903)	(1,131,306)
Consolidated Statement of Operations [Abstract]
Interest expense							(9,349)	(9,510)	$ (12,440)
Loss on early retirement of debt							(8,627)	0	(66,196)
Income (loss) before income tax benefit (expense)							(29,148)	(134,552)	338,766
Income tax expense							551	(345,191)	(51,507)
Net income (loss)			224,613		(355,687)		(28,597)	(479,743)	287,259
Net income (loss) attributable to Ionis Pharmaceuticals, Inc. common stockholders			$ 224,613		$ (354,532)		$ (28,597)	$ (444,263)	$ 278,143
Basic net loss per share (in dollars per share) | $ / shares			$ 1.59	[1],[2]	$ (2.54)	[1],[2]	$ (0.20)	$ (3.18)	$ 2.00
Diluted net loss per share (in dollars per share) | $ / shares			$ 1.41	[1],[3]	$ (2.54)	[1]	$ (0.20)	$ (3.18)	$ 1.90
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		$ 1,577,459	$ 771,737		$ 743,282		$ 771,737	$ 743,282	$ 1,577,459		$ 1,100,623
Additional Paid In Capital [Member]
Consolidated Statement of Operations [Abstract]
Net income (loss) attributable to Ionis Pharmaceuticals, Inc. common stockholders							0	0	0
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		1,985,650	1,964,167		1,895,519		1,964,167	1,895,519	1,985,650		1,833,668
Accumulated Deficit [Member]
Consolidated Statement of Operations [Abstract]
Net income (loss) attributable to Ionis Pharmaceuticals, Inc. common stockholders							(28,597)	(444,263)	278,143
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		(596,495)	(1,159,903)		(1,131,306)		(1,159,903)	(1,131,306)	(596,495)		(840,251)
Total Ionis Stockholders' Equity [Member]
Consolidated Statement of Operations [Abstract]
Net income (loss) attributable to Ionis Pharmaceuticals, Inc. common stockholders							(28,597)	(444,263)	278,143
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		$ 1,364,005	$ 771,737		$ 743,282		$ 771,737	$ 743,282	$ 1,364,005		$ 961,539
0.125 Percent Convertible Senior Notes [Member]
Convertible Debt [Abstract]
Interest rate on convertible senior notes		0.125%	0.125%		0.125%		0.125%	0.125%	0.125%
Consolidated Balance Sheet [Abstract]
Convertible senior notes			$ 542,314		$ 540,136		$ 542,314	$ 540,136
Consolidated Statement of Operations [Abstract]
Effective interest rate			0.50%				0.50%
1 Percent Convertible Senior Notes [Member]
Convertible Debt [Abstract]
Interest rate on convertible senior notes	1.00%	1.00%	1.00%		1.00%		1.00%	1.00%	1.00%	1.00%		1.00%	1.00%
Face amount of offering												$ 185,500	$ 500,000
Consolidated Statement of Operations [Abstract]
Loss on early retirement of debt	$ 8,600	$ (66,200)
Effective interest rate			1.40%				1.40%
0 Percent Convertible Senior Notes [Member]
Convertible Debt [Abstract]
Interest rate on convertible senior notes	0.00%	0.00%	0.00%				0.00%		0.00%
Face amount of offering	$ 632,500
Consolidated Balance Sheet [Abstract]
Convertible senior notes			$ 619,119		$ 0		$ 619,119	$ 0
Consolidated Statement of Operations [Abstract]
Effective interest rate			0.50%				0.50%
As Previously Reported [Member]
Consolidated Balance Sheet [Abstract]
1 percent convertible senior notes, net					293,161			293,161
Additional paid-in capital					2,113,646			2,113,646
Accumulated deficit					(1,249,368)			(1,249,368)
Consolidated Statement of Operations [Abstract]
Interest expense								(44,990)	$ (48,768)
Loss on early retirement of debt									(21,865)
Income (loss) before income tax benefit (expense)								(170,032)	346,769
Income tax expense								(316,734)	(43,507)
Net income (loss)								(486,766)	303,262
Net income (loss) attributable to Ionis Pharmaceuticals, Inc. common stockholders								$ (451,286)	$ 294,146
Basic net loss per share (in dollars per share) | $ / shares								$ (3.23)	$ 2.12
Diluted net loss per share (in dollars per share) | $ / shares								$ (3.23)	$ 2.08
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		$ 1,684,547			843,347			$ 843,347	$ 1,684,547
As Previously Reported [Member] | Additional Paid In Capital [Member]
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		2,203,778			2,113,646			2,113,646	2,203,778
As Previously Reported [Member] | Accumulated Deficit [Member]
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		(707,534)			(1,249,368)			(1,249,368)	(707,534)
As Previously Reported [Member] | 0.125 Percent Convertible Senior Notes [Member]
Consolidated Balance Sheet [Abstract]
Convertible senior notes					455,719			455,719
Adjustment [Member] | ASU 2020-06 [Member]
Consolidated Balance Sheet [Abstract]
1 percent convertible senior notes, net					15,648			15,648
Additional paid-in capital					(218,127)			(218,127)
Accumulated deficit					118,062			118,062
Net deferred tax assets					0			0
Consolidated Statement of Operations [Abstract]
Interest expense								35,480	36,328
Loss on early retirement of debt									(44,331)
Income (loss) before income tax benefit (expense)								35,480	(8,003)
Income tax expense								(28,457)	(8,000)
Net income (loss)								7,023	(16,003)
Net income (loss) attributable to Ionis Pharmaceuticals, Inc. common stockholders								$ 7,023	$ (16,003)
Basic net loss per share (in dollars per share) | $ / shares								$ 0.05	$ (0.12)
Diluted net loss per share (in dollars per share) | $ / shares								$ 0.05	$ (0.18)
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		(107,088)			(100,065)			$ (100,065)	$ (107,088)
Adjustment [Member] | ASU 2020-06 [Member] | Additional Paid In Capital [Member]
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		(218,128)			(218,127)			(218,127)	(218,128)
Adjustment [Member] | ASU 2020-06 [Member] | Accumulated Deficit [Member]
Consolidated Statements of Stockholders' Equity [Abstract]
Balance		$ 111,039			118,062			118,062	$ 111,039
Adjustment [Member] | ASU 2020-06 [Member] | 0.125 Percent Convertible Senior Notes [Member]
Consolidated Balance Sheet [Abstract]
Convertible senior notes					$ 84,417			$ 84,417

[1] We compute net income (loss) per share independently for each quarter during the year.

[2] As discussed in Note 1, Organization and Significant Accounting Policies, we compute basic net income (loss) per share by dividing the total net income (loss) attributable to our common stockholders by our weighted-average number of common shares outstanding during the period. Our basic net income per share for the fourth quarter of 2021 was $1.59.Our basic net loss per share calculation for the fourth quarter of 2020 considered our net loss for Ionis on a stand-alone basis plus our share of Akcea’s net loss for the period. To calculate the portion of Akcea’s net loss attributable to our ownership, we multiplied Akcea’s loss per share by the weighted average shares we owned in Akcea during the period. As a result of this calculation, our total net loss available to Ionis common stockholders for the calculation of net loss per share is different than net loss attributable to Ionis Pharmaceuticals, Inc. common stockholders in the consolidated statements of operations.

[3] We had net income available to Ionis common stockholders for the fourth quarter of 2021. As a result, we computed diluted net income per share using the weighted-average number of common shares and dilutive common equivalent shares outstanding during the period