Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net income (loss)	$ (18,742)	$ 35,679
Adjustments to reconcile net income to net cash used in operating activities
Depreciation and amortization	15,970	13,531
Provision for severance benefits	9,165	10,776
Amortization of debt issuance costs and original issue discount	1,073	950
Loss (gain) on foreign currency, net	32,369	(35,813)
Restructuring and other gain		(17,010)
Stock-based compensation	2,810	1,179
Other	1,053	220
Changes in operating assets and liabilities
Accounts receivable, net	5,305	(9,730)
Unbilled accounts receivable	887
Inventories, net	(16,797)	2,646
Other receivables	(4,508)	2,598
Other current assets	2,253	1,135
Accounts payable	(4,473)	(1,919)
Other accounts payable	(5,229)	(7,790)
Accrued expenses	(1,435)	(10,776)
Deferred revenue	5,413	(265)
Other current liabilities	760	(436)
Other non-current liabilities	1,116	(268)
Payment of severance benefits	(5,754)	(18,082)
Other	516	(107)
Net cash provided by (used in) operating activities	21,752	(33,482)
Cash flows from investing activities
Proceeds from settlement of hedge collateral	4,863	6,781
Payment of hedge collateral	(7,490)	(10,036)
Proceeds from disposal of plant, property and equipment	13	1,125
Purchase of plant, property and equipment	(11,432)	(10,807)
Payment for property related to water treatment facility arrangement	(4,283)
Payment for intellectual property registration	(574)	(566)
Collection of guarantee deposits	659	1,400
Payment of guarantee deposits		(41)
Other	(38)	22
Net cash used in investing activities	(18,282)	(12,122)
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	435	2,525
Acquisition of treasury stock		(11,401)
Proceeds from property related to water treatment facility arrangement	4,283
Net cash provided by financing activities	4,718	71,472
Effect of exchange rates on cash, cash equivalents and restricted cash	(5,081)	4,049
Net increase in cash, cash equivalents and restricted cash	3,107	29,917
Cash, cash equivalents and restricted cash
Beginning of the period	128,575	101,606
End of the period	131,682	131,523
Supplemental cash flow information
Cash paid for interest	9,609	7,980
Cash paid for income taxes	668	790
Non-cash investing and financing activities
Property, plant and equipment additions in other accounts payable	2,582	$ 2,092
Acquisition of treasury stock to satisfy the tax withholding obligations in connection with equity- based compensation	$ (199)