Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income (loss)	$ 84,936	$ (29,615)	$ (84,867)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities
Depreciation and amortization	28,146	25,416	26,490
Provision for severance benefits	24,373	14,432	15,289
Amortization of debt issuance costs and original issue discount	1,987	707	660
Loss (gain) on foreign currency, net	(77,600)	18,884	46,984
Restructuring gain and other	(17,010)	(7,785)
Stock-based compensation	2,336	3,843	2,768
Other	49	103	2,434
Changes in operating assets and liabilities
Accounts receivable, net	(22,210)	285	3,299
Inventories, net	(8,077)	(557)	12,929
Other receivables	3,981	19,125	(21,463)
Other current assets	2,318	5,000	11,339
Accounts payable	10,320	(4,163)	(12,605)
Other accounts payable	(12,141)	(6,603)	(10,892)
Accrued expenses	(12,020)	(16,305)	(1,679)
Deferred revenue	(3,949)	1,674	8,136
Other current liabilities	(1,281)	(5,331)	(1,210)
Other non-current liabilities	(760)	(1,574)	3,105
Payment of severance benefits	(21,506)	(15,352)	(11,394)
Other (Note 19)	(336)	5,447	700
Net cash provided by (used in) operating activities	(18,444)	7,631	(9,977)
Cash flows from investing activities
Proceeds from settlement of hedge collateral	10,615	6,317	10,841
Payment of hedge collateral	(14,839)	(3,552)	(17,182)
Proceeds from disposal of plant, property and equipment	18,834	688	9,886
Purchase of property, plant and equipment	(32,661)	(18,727)	(6,350)
Payment for intellectual property registration	(1,207)	(1,049)	(742)
Collection of guarantee deposits	1,462	619	636
Payment of guarantee deposits	(41)	(193)	(675)
Other	94	23	195
Net cash used in investing activities	(17,743)	(15,874)	(3,391)
Cash flows from financing activities
Proceeds from issuance of senior notes	86,250
Payment of debt issuance costs	(5,902)
Proceeds from exercise of stock options	3,744	1,732	3,436
Acquisition of treasury stock	(11,401)
Net cash provided by financing activities	72,691	1,732	3,436
Effect of exchange rates on cash and cash equivalents	8,716	(1,016)	(1,620)
Net increase (decrease) in cash and cash equivalents	45,220	(7,527)	(11,552)
Cash and cash equivalents
Beginning of the period	83,355	90,882	102,434
End of the period	128,575	83,355	90,882
Supplemental cash flow information
Cash paid for interest	17,590	14,906	15,181
Cash paid (refunded) for income taxes	1,027	693	(5,276)
Non-cash investing and financing activities
Property, plant and equipment additions in other accounts payable	$ 2,520	3,091	$ 3,348
Restricted cash received from sale of property, plant and equipment		$ (16,917)