Condensed Consolidated Statements of Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Tax on unrealized gain on short-term investments	$ 0	$ 0	$ 0	$ 0
Tax on unrealized gains on foreign currency translation	$ 0	$ 0	$ 0	$ 0