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.

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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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- Definition

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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- Definition

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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Significant Accounting Policies, Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 34,883	$ 21,472	$ 97,210	$ 63,642
Research, Development and Patent [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	18,780	16,181	57,698	48,443
Selling, General and Administrative [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	16,103	5,291	$ 39,512	$ 15,199
Employee Stock Options [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate			2.30%	1.80%
Dividend yield			0.00%	0.00%
Volatility			63.10%	66.10%
Expected life			4 years 7 months 6 days	4 years 6 months
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation expense related to non-vested stock options	139,500		$ 139,500
Weighted average period for recognition			1 year 3 months 18 days
Board of Director Stock Options [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate			2.80%	2.20%
Dividend yield			0.00%	0.00%
Volatility			61.50%	61.20%
Expected life			6 years 7 months 6 days	6 years 7 months 6 days
ESPP [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate			1.80%	0.80%
Dividend yield			0.00%	0.00%
Volatility			47.30%	59.90%
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	32,600		$ 32,600
Weighted average period for recognition			1 year 7 months 6 days
RSUs [Member] \| Employees [Member]
Stock-based Compensation Expense [Abstract]
Weighted-average grant date fair value (in dollars per share)			$ 51.83
RSUs [Member] \| Board of Directors [Member]
Stock-based Compensation Expense [Abstract]
Weighted-average grant date fair value (in dollars per share)			$ 42.88
Akcea [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 12,700	$ 4,700	$ 31,200	$ 11,800