Significant Accounting Policies, Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	May 31, 2019
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 41,933	$ 33,876	$ 87,437	$ 62,327
Employee Stock Options [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate			2.40%	2.30%
Dividend yield			0.00%	0.00%
Volatility			60.30%	63.10%
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	162,700		$ 162,700
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			2.00%
Dividend yield			0.00%
Volatility			60.60%
Expected life			6 years 8 months 12 days
Stock-based Compensation Expense [Abstract]
Options granted (in shares)				0
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	$ 61,300		$ 61,300
Weighted average period for recognition			1 year 9 months 18 days
RSUs [Member] | Employees [Member]
Stock-based Compensation Expense [Abstract]
Weighted-average grant date fair value (in dollars per share)			$ 59.27
RSUs [Member] | Board of Directors [Member]
Stock-based Compensation Expense [Abstract]
Weighted-average grant date fair value (in dollars per share)			$ 63.90
2011 Equity Incentive Plan [Member]
Amendment to Equity Plan [Abstract]
Common shares reserved for future issuance (in shares)	23,000,000		23,000,000		16,000,000
Cost of Products Sold [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 137	0	$ 255	$ 0
Research, Development and Patent [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	23,756	19,236	48,191	38,918
Selling, General and Administrative [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 18,040	$ 14,640	$ 38,991	$ 23,409
Akcea [Member] | Employee Stock Options [Member]
Weighted-Average Assumptions [Abstract]
Risk-free interest rate			2.50%	2.80%
Dividend yield			0.00%	0.00%
Volatility			76.30%	77.70%
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			1.90%	2.90%
Dividend yield			0.00%	0.00%
Volatility			74.30%	78.20%
Expected life			6 years 3 months 18 days	6 years 4 months 24 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