Significant Accounting Policies, Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 40,790	$ 45,505
Cost of Products Sold [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	237	118
Research, Development and Patent [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	25,556	24,435
Selling, General and Administrative [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 14,997	$ 20,952
Employee Stock Options [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate	1.60%	2.40%
Dividend yield	0.00%	0.00%
Volatility	58.90%	60.30%
Expected life	4 years 8 months 12 days	4 years 7 months 6 days
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation expense related to non-vested stock options	$ 146,300
Weighted average period for recognition	1 year 4 months 24 days
ESPP [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate	1.10%	2.50%
Dividend yield	0.00%	0.00%
Volatility	47.20%	45.50%
Expected life	6 months	6 months
RSUs [Member]
Weighted-Average Assumptions [Abstract]
Vesting period	4 years
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost related to non-vested RSUs	$ 114,300
Weighted average period for recognition	1 year 10 months 24 days
RSUs [Member] \| Employees [Member]
Weighted-Average Assumptions [Abstract]
Weighted-average grant date fair value (in dollars per share)	$ 62.30
Akcea [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 7,300	$ 18,600
Akcea [Member] \| Employee Stock Options [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate	1.50%	2.50%
Dividend yield	0.00%	0.00%
Volatility	73.60%	76.40%
Expected life	6 years 1 month 6 days	6 years 1 month 6 days
Akcea [Member] \| Board of Director Stock Options [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate	1.50%
Dividend yield	0.00%
Volatility	73.30%
Expected life	6 years 3 months 18 days
Akcea [Member] \| ESPP [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate	1.00%	2.50%
Dividend yield	0.00%	0.00%
Volatility	71.90%	64.10%
Expected life	6 months	6 months
Akcea [Member] \| RSUs [Member] \| Employees [Member]
Weighted-Average Assumptions [Abstract]
Weighted-average grant date fair value (in dollars per share)	$ 15.84
Akcea [Member] \| RSUs [Member] \| Minimum [Member]
Weighted-Average Assumptions [Abstract]
Vesting period	6 months
Akcea [Member] \| RSUs [Member] \| Maximum [Member]
Weighted-Average Assumptions [Abstract]
Vesting period	4 years

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Amount of cost to be recognized for option under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Rate of weighted-average expected volatility for award under share-based payment arrangement.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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