Income Taxes, Reconciliation of Statutory to Effective Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation Between Effective and Statutory Tax Rate [Abstract]
Pre-tax loss	$ (23,276)	$ (83,622)	$ (87,906)
Statutory rate	(8,147)	(29,268)	(30,767)
State income tax net of federal benefit	722	(276)	1
Foreign	4,299	0	0
Net change in valuation allowance	(76,409)	55,927	69,499
Net operating loss expiration	3,987	0	0
Tax credits	(32,769)	(26,954)	(41,284)
Deferred tax true-up	4,848	2,591	1,496
Tax Cuts and Jobs Act	107,323	0	0
Nondeductible items	4,123	1,149	1,055
Akcea deconsolidation adjustment at IPO	469	0	0
Excess stock-based compensation	(14,337)	0	0
Other	(89)	(235)	372
Income tax (benefit) expense	$ (5,980)	$ 2,934	$ 372
Reconciliation Between Effective and Statutory Tax Rate Percentage [Abstract]
Statutory rate	35.00%	35.00%	35.00%
State income tax net of federal benefit	(3.10%)	0.30%	0.00%
Foreign	(18.30%)	0.00%	0.00%
Net change in valuation allowance	328.30%	(66.90%)	(79.10%)
Net operating loss expiration	(17.00%)	0.00%	0.00%
Tax credits	140.80%	32.20%	47.00%
Deferred tax true-up	(20.60%)	(3.10%)	(1.70%)
Tax Cuts and Jobs Act	(461.10%)	0.00%	0.00%
Nondeductible items	(17.90%)	(1.40%)	(1.20%)
Akcea deconsolidation adjustment at IPO	(2.00%)	0.00%	0.00%
Excess stock-based compensation	61.00%	0.00%	0.00%
Other	0.60%	0.40%	(0.40%)
Effective rate	25.70%	(3.50%)	(0.40%)