Operating Leases (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2019 USD ($) Option	Mar. 31, 2018 USD ($)
Operating Leases [Abstract]
Right-of-use operating lease assets	[1]	$ 13,100
Operating lease liabilties	[2]	$ 17,960
Weighted average remaining lease term		9 years
Weighted average discount rate		7.60%
Current portion of operating lease liabilties		$ 2,000
Operating lease cash payments		1,000
Annual Future Minimum Payments Under Operating Leases [Abstract]
Remainder of 2019		2,341
2020		3,008
2021		2,725
2022		2,539
2023		2,505
Thereafter		11,862
Total minimum payments		24,980
Imputed interest		(7,020)
Total lease liabilities	[2]	17,960
Rent expense		$ 900	$ 0
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
Office Space Subleased to Akcea [Member]
Operating Leases [Abstract]
Number of options to extend lease | Option		1
Term of lease extension		5 years
Akcea [Member] | Office Space for Corporate Headquarters [Member]
Operating Leases [Abstract]
Term of lease extension		5 years
Term of lease		123 months
Period of free rent under lease		3 months
Tenant improvement allowance		$ 3,800
Initial amount of letter of credit		2,400
Letter of credit on third anniversary of rent commencement date		1,800
Letter of credit on fifth anniversary of rent commencement date		$ 1,200

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

[2] Current portion of $2.0 million was included in current portion of long-term obligations on our condensed consolidated balance sheet, with the difference included in long-term obligations.