Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 131,682	$ 128,575
Accounts receivable, net	85,570	92,026
Unbilled accounts receivable	35,857
Inventories, net	57,456	73,073
Other receivables	8,468	4,292
Prepaid expenses	10,227	9,250
Hedge collateral (Note 7)	10,100	7,600
Other current assets (Notes 7 and 18)	11,023	15,444
Total current assets	350,383	330,260
Property, plant and equipment, net	197,034	205,903
Intangible assets, net	3,966	4,061
Long-term prepaid expenses	13,858	12,791
Other non-current assets	5,851	5,774
Total assets	571,092	558,789
Current liabilities
Accounts payable	60,742	65,940
Other accounts payable	11,123	10,261
Accrued expenses	49,506	51,746
Deferred revenue	13,440	8,335
Other current liabilities (Note 7)	5,149	1,860
Total current liabilities	139,960	138,142
Long-term borrowings, net	304,489	303,416
Accrued severance benefits, net	145,542	148,905
Other non-current liabilities (Note 4)	14,894	7,963
Total liabilities	604,885	598,426
Commitments and contingencies (Note 18)
Stockholders' equity
Common stock, $0.01 par value, 150,000,000 shares authorized, 42,877,395 shares issued and 34,483,754 outstanding at June 30, 2018 and 42,563,808 shares issued and 34,189,599 outstanding at December 31, 2017	429	426
Additional paid-in capital	139,502	136,259
Accumulated deficit	(51,147)	(40,889)
Treasury stock, 8,393,641shares at June 30, 2018 and 8,374,209 shares at December 31, 2017	(102,518)	(102,319)
Accumulated other comprehensive loss	(20,059)	(33,114)
Total stockholders' deficit	(33,793)	(39,637)
Total liabilities and stockholders' equity	$ 571,092	$ 558,789