Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Inventory cost	$ 7,974	$ 8,000
Accrued expenses and accounts receivable	1,866	690
Foreign tax credits	17,600	10,626
Research and development tax credits	15,456	15,828
Net operating loss carryforwards	9,635	5,392
Accrued pension	4,294	5,428
Share based compensation and others	9,972	12,443
Total deferred tax assets, include valuation allowance	66,797	58,407
Valuation allowances	(25,941)	(22,560)
Total deferred tax assets, non-current	40,856	35,847
Deferred tax liabilities
Plant, equipment and intangible assets	(16,661)	(17,278)
Outside basis differences and others	(7,267)
Total deferred tax liabilities, non-current	(23,928)	(17,278)
Net deferred tax assets	$ 16,928	$ 18,569