Summary of Significant Accounting Policies - Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended		24 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Research and development incentive income and receivable
Research and development expenses reimbursed (as a percent)	43.50%	45.00%
Research and development incentive income and receivable
Balance at the beginning of the period	$ 3,053
Australian research and development incentive income	1,715	$ 3,129
Refund for 2016 eligible expenses	(3,245)
Foreign currency translation	221	(76)
Balance at the end of the period	1,744	3,053	$ 1,744
Overseas research and development incentive income		717
Income Taxes
Uncertain tax positions	0	0	0
Interest and penalties pertaining to uncertain tax positions	0	0	0
Other Assets
Other assets	$ 1,111	$ 907	$ 1,111
Computer office 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