CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net income (loss)	$ 278,384	$ (45,252)
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Depreciation and amortization	13,333	24,661
Provision for severance benefits	14,150	10,491
Amortization of debt issuance costs and original issue discount	1,824	1,712
Loss on foreign currency, net	6,609	50,512
Restructuring and other charges	490	470
Provision for inventory reserves	4,079	9,255
Stock-based compensation	4,754	1,920
Loss on early extinguishment of long-term borrowings, net		42
Gain on sale of discontinued operations	(287,117)
Others, net	85	61
Changes in operating assets and liabilities
Accounts receivable, net	(16,583)	(32,812)
Unbilled accounts receivable, net	14,260	14,208
Inventories	1,390	(15,576)
Other receivables	6,111	(4,814)
Other current assets	9,143	6,356
Accounts payable	(5,156)	27,585
Other accounts payable	(8,034)	(10,074)
Accrued expenses	1,991	3,831
Accrued income taxes	12,546	(583)
Other current liabilities	2,243	(5,766)
Other non-current liabilities	2,868	808
Payment of severance benefits	(5,888)	(6,195)
Others, net	59	(821)
Net cash provided by operating activities	51,541	30,019
Cash flows from investing activities
Proceeds from settlement of hedge collateral	8,029	12,625
Payment of hedge collateral	(7,841)	(17,024)
Purchase of property, plant and equipment	(16,353)	(16,693)
Payment for intellectual property registration	(664)	(907)
Collection of guarantee deposits	891	539
Payment of guarantee deposits	(611)	(1,330)
Proceeds from sale of discontinued operations	350,553
Others, net	26	225
Net cash provided by (used in) investing activities	334,030	(22,565)
Cash flows from financing activities
Repurchase of long-term borrowings		(1,175)
Proceeds from exercise of stock options	2,690	1,038
Acquisition of treasury stock	(1,021)	(2,588)
Repayment of financing related to water treatment facility arrangement	(402)	(415)
Repayment of principal portion of finance lease liabilities	(165)	(174)
Net cash provided by (used in) financing activities	1,102	(3,314)
Effect of exchange rates on cash and cash equivalents	3,781	(5,237)
Net increase (decrease) in cash and cash equivalents	390,454	(1,097)
Cash and cash equivalents
Beginning of the period	151,657	132,438
End of the period	542,111	131,341
Supplemental cash flow information
Cash paid for interest	19,044	19,071
Cash paid for income taxes	2,573	1,904
Non-cash investing activities
Property, plant and equipment additions in other accounts payable	$ 3,865	$ 496