Consolidated Statements of Shareholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Ordinary shares	Preferred Stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive loss	Treasury Shares
Beginning balance (in shares) at Dec. 31, 2017		41,463	0				2,117
Beginning balance at Dec. 31, 2017	$ 85,580	$ 414	$ 0	$ 393,478	$ (262,685)	$ (23,266)	$ (22,361)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(95,304)				(95,304)
Other comprehensive income (loss)	(150)					(150)
Exercise of stock options (in shares)		82
Exercise of stock options	535	$ 1		534
Exercise of warrants (in shares)		603
Exercise of warrants	2,911	$ 6		2,905
Expiration of warrants	2,167			2,167
Vesting of restricted shares (in shares)		547
Vesting of restricted shares	0	$ 6		(6)
Employee share purchase plan share issuance (in shares)		25
Employee share purchase plan share issuance	127			127
Share-based compensation expense	7,852			7,852
Equity component of 2023 Notes	26,699			26,699
Share repurchases (in shares)							3,290
Share repurchases	(27,637)						$ (27,637)
Ending balance (in shares) at Dec. 31, 2018		42,720	0				5,407
Ending balance at Dec. 31, 2018	2,780	$ 427	$ 0	433,756	(357,989)	(23,416)	$ (49,998)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(33,226)				(33,226)
Other comprehensive income (loss)	610					610
Vesting of restricted shares (in shares)		153
Vesting of restricted shares	0	$ 2		(2)
Employee share purchase plan share issuance (in shares)		54
Employee share purchase plan share issuance	118			118
Share-based compensation expense	519			519
Ending balance (in shares) at Dec. 31, 2019		42,927	0				5,407
Ending balance at Dec. 31, 2019	(29,199)	$ 429	$ 0	434,391	(391,215)	(22,806)	$ (49,998)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	7,028				7,028
Other comprehensive income (loss)	$ 1,755					1,755
Exercise of stock options (in shares)	403	403
Exercise of stock options	$ 2,045	$ 4		2,041
February 2020 private placement (in shares)		8,680	488
February 2020 private placement	60,570	$ 87	$ 5	60,478
May 2020 public offering (in shares)		11,630
May 2020 public offering	116,924	$ 116		116,808
Vesting of restricted shares (in shares)		114
Vesting of restricted shares	0	$ 1		(1)
Employee share purchase plan share issuance (in shares)		49
Employee share purchase plan share issuance	144			144
Share-based compensation expense	2,999			2,999
Retirement of treasury shares (in shares)		(5,407)					(5,407)
Retirement of treasury shares	0	$ (54)		(49,944)			$ (49,998)
Ending balance (in shares) at Dec. 31, 2020		58,396	488				0
Ending balance at Dec. 31, 2020	$ 162,266	$ 583	$ 5	$ 566,916	$ (384,187)	$ (21,051)	$ 0