Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance at Dec. 31, 2017	$ 269	$ 294,613	$ (201,541)	$ (5,712)	$ 87,629
Exercise of share options	7	3,234			3,241
Share-based compensation expense		5,551			5,551
Tax on vesting of restricted share units		(383)			(383)
Other comprehensive income (loss),				(2,811)	(2,811)
Net income (loss)			120,779		120,779
Balance at Dec. 31, 2018	276	303,015	(80,762)	(8,523)	214,006
Exercise of share options	4	4,031			4,035
Share-based compensation expense		3,613			3,613
Tax on vesting of restricted share units		(224)			(224)
Other comprehensive income (loss),				1,062	1,062
Net income (loss)			(1,809)		(1,809)
Ordinary shares repurchased	(4)	(5,526)	(1,462)		(6,992)
Balance at Dec. 31, 2019	$ 276	$ 304,909	$ (84,033)	$ (7,461)	$ 213,691