Summary of Significant Accounting Policies - Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Research and development incentive income and receivable
Research and development expenses reimbursed (as a percent)	43.50%	43.50%
Research and development incentive income and receivable
Balance at the beginning of the period	$ 1,744	$ 3,053
Australian research and development incentive income	756	1,715
Cash receiver for eligible expenses	(793)	(3,245)
Cash received for 2016 eligible overseas research and development expenses	(740)
Foreign currency translation	(131)	221
Balance at the end of the period	836	1,744	$ 3,053
Overseas research and development incentive income			$ 717
Uncertain Tax Positions
Uncertain tax positions	0	0
Interest and penalties pertaining to uncertain tax positions	0	0
Other Assets
Other assets	1,380	$ 1,111
Deferred issuance costs	$ 162
Computer equipment
Property and Equipment
Useful life (in years)	3 years
Lab equipment
Property and Equipment
Useful life (in years)	5 years
Office equipment
Property and Equipment
Useful life (in years)	5 years
Furnitures and fixtures
Property and Equipment
Useful life (in years)	5 years