Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				6 Months Ended
	Jun. 30, 2018	Apr. 30, 2018	Mar. 31, 2018	Jan. 31, 2018	Jun. 30, 2018	Jun. 30, 2017
Common Shares [Line Items]
Issuance price per share	$ 45.00				$ 45.00
Proceeds from issuance of common shares	$ 49,889				$ 55,000	$ 179,996
Other offering expenses	$ 111				$ 2,987	$ 3,053
Private Placement
Common Shares [Line Items]
Common stock sold (shares)			2,000,000
Issuance price per share			$ 27.50
Net proceeds from private placement stock issuance			$ 52,000
Underwriting discounts and commissions			2,800
Other offering expenses			200
BMS Agreement
Common Shares [Line Items]
Upfront payment under the BMS Amendment			$ 50,000
ALS Biopharma
Common Shares [Line Items]
Exercise of warrants, net settlement of shares		325,000		275,000
Number of shares issued for exercise of warrants		261,140		228,219
RPI Purchase Agreement
Common Shares [Line Items]
Common stock sold (shares)	1,111,111
Proceeds from issuance of common shares	$ 50,000