Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock/Ordinary Shares	Additional paid in capital	Accumulated other comprehensive income	Accumulated deficit	Total
Stockholders' equity, beginning balance at Dec. 31, 2018	$ 670	$ 461,911	$ 27	$ (393,978)	$ 68,630
Stockholders' equity, beginning balance (in shares) at Dec. 31, 2018	67,019
Consolidated Statements of Changes in Stockholders’ Equity
Issuance of ordinary shares	$ 43	10,014			10,057
Issuance of ordinary shares (in shares)	4,317
Equity transaction costs		(270)			(270)
Stock-based compensation expense		1,907			1,907
Net loss				(20,217)	(20,217)
Stockholders' equity, ending balance at Mar. 31, 2019	$ 713	473,562	27	(414,195)	60,107
Stockholders' equity, ending balance (in shares) at Mar. 31, 2019	71,336
Stockholders' equity, beginning balance at Dec. 31, 2018	$ 670	461,911	27	(393,978)	68,630
Stockholders' equity, beginning balance (in shares) at Dec. 31, 2018	67,019
Stockholders' equity, ending balance at Dec. 31, 2019	$ 945	517,044	27	(476,742)	41,274
Stockholders' equity, ending balance (in shares) at Dec. 31, 2019	94,545
Consolidated Statements of Changes in Stockholders’ Equity
Issuance of ordinary shares	$ 5	181			186
Issuance of ordinary shares (in shares)	479
Shares issued in connection with the vesting of restricted stock units	$ 1	(1)
Shares issued in connection with the vesting of restricted stock units (in shares)	85
Equity transaction costs		(39)			(39)
Stock-based compensation expense		1,752			1,752
Net loss				(23,259)	(23,259)
Stockholders' equity, ending balance at Mar. 31, 2020	$ 951	$ 518,937	$ 27	$ (500,001)	$ 19,914
Stockholders' equity, ending balance (in shares) at Mar. 31, 2020	95,109