Significant Accounting Policies, Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 45,505	$ 28,451
Employee Stock Options [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate	2.40%	2.20%
Dividend yield	0.00%	0.00%
Volatility	60.30%	63.20%
Expected life	4 years 7 months 6 days	4 years 7 months 6 days
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation expense related to non-vested stock options	$ 192,200
Weighted average period for recognition	1 year 4 months 24 days
ESPP [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate	2.50%	1.60%
Dividend yield	0.00%	0.00%
Volatility	45.50%	44.40%
Expected life	6 months	6 months
RSUs [Member]
Stock-based Compensation Expense [Abstract]
Vesting period	4 years
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost related to non-vested RSUs	$ 68,700
Weighted average period for recognition	2 years
RSUs [Member] \| Employees [Member]
Stock-based Compensation Expense [Abstract]
Weighted-average grant date fair value (in dollars per share)	$ 58.26
Cost of Products Sold [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 118	$ 0
Research, Development and Patent [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	24,435	19,682
Selling, General and Administrative [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	20,952	8,769
Akcea [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 18,600	$ 6,400
Akcea [Member] \| Employee Stock Options [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate	2.50%	2.60%
Dividend yield	0.00%	0.00%
Volatility	76.40%	77.10%
Expected life	6 years 1 month 6 days	6 years 1 month 6 days
Akcea [Member] \| ESPP [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate	2.50%	1.60%
Dividend yield	0.00%	0.00%
Volatility	64.10%	62.30%
Expected life	6 months	6 months

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Unrecognized cost of unvested options awarded to employees as compensation.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Weighted average expected volatility rate of share-based compensation awards.

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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 share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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