Operating Leases (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Option	Sep. 30, 2018 USD ($)
Operating Leases [Abstract]
Right-of-use operating lease assets	[1]	$ 13,000		$ 13,000
Operating lease liabilities	[2]	$ 17,731		$ 17,731
Weighted average remaining lease term		8 years 3 months 18 days		8 years 3 months 18 days
Weighted average discount rate		7.50%		7.50%
Current portion of operating lease liabilties		$ 2,100		$ 2,100
Operating lease cash payments				2,900
Annual Future Minimum Payments Under Operating Leases [Abstract]
Remainder of 2019		801		801
2020		3,282		3,282
2021		3,019		3,019
2022		2,781		2,781
2023		2,520		2,520
Thereafter		11,861		11,861
Total minimum lease payments		24,264		24,264
Imputed interest		(6,533)		(6,533)
Total operating lease liabilities	[2]	17,731		17,731
Rent expense		$ 800	$ 1,000	$ 2,700	$ 1,800
Office and Laboratory Space Adjacent to Manufacturing Facility [Member]
Operating Leases [Abstract]
Number of options to extend lease | Option				2
Term of lease extension		5 years		5 years
Office Space Subleased to Akcea [Member]
Operating Leases [Abstract]
Number of options to extend lease | Option				1
Term of lease extension		5 years		5 years
Akcea [Member] | Office Space for Corporate Headquarters [Member]
Operating Leases [Abstract]
Term of lease extension		5 years		5 years
Term of lease		123 months		123 months
Period of free rent under lease				3 months
Tenant improvement allowance		$ 3,800		$ 3,800
Initial amount of letter of credit		2,400		2,400
Letter of credit on third anniversary of rent commencement date		1,800		1,800
Letter of credit on fifth anniversary of rent commencement date		$ 1,200		$ 1,200

[1] Included in deposits and other assets on our condensed consolidated balance sheet.

[2] Current portion of $2.1 million was included in current portion of long-term obligations on our condensed consolidated balance sheet, with the difference included in long-term obligations.