CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets
Cash and cash equivalents	$ 284,921	$ 279,547
Accounts receivable, net	51,208	50,954
Inventories, net	36,947	39,370
Other receivables (Notes 16 and 18)	26,121	25,895
Prepaid expenses	9,124	7,675
Hedge collateral (Note 7)	4,060	3,060
Other current assets (Note 17)	9,262	2,619
Total current assets	421,643	409,120
Property, plant and equipment, net	102,675	107,882
Operating lease right-of-use assets	3,719	4,275
Intangible assets, net	2,203	2,377
Long-term prepaid expenses	6,771	8,243
Deferred income taxes	40,246	41,095
Other non-current assets	10,608	10,662
Total assets	587,865	583,654
Current liabilities
Accounts payable	37,566	37,593
Other accounts payable	7,707	6,289
Accrued expenses (Note 6)	20,573	20,071
Accrued income taxes	9,361	11,823
Operating lease liabilities	2,223	2,323
Other current liabilities	6,989	7,382
Total current liabilities	84,419	85,481
Accrued severance benefits, net	32,572	33,064
Non-current operating lease liabilities	1,496	1,952
Other non-current liabilities	8,216	10,395
Total liabilities	126,703	130,892
Commitments and contingencies (Note 17)
Stockholders' equity
Common stock, $0.01 par value, 150,000,000 shares authorized, 56,225,441 shares issued and 44,894,385 outstanding at March 31, 2022 and 55,905,320 shares issued and 45,659,304 outstanding at December 31, 2021	562	559
Additional paid-in capital	261,830	241,197
Retained earnings	353,070	343,542
Treasury stock, 11,331,056 shares at March 31, 2022 and 10,246,016 shares at December 31, 2021, respectively	(148,523)	(130,306)
Accumulated other comprehensive loss	(5,777)	(2,230)
Total stockholders' equity	461,162	452,762
Total liabilities and stockholders' equity	$ 587,865	$ 583,654