Amkor Technology (AMKR) 10-K 23 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 16, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	AMKOR TECHNOLOGY, INC.
Entity Central Index Key	1,047,127
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		239,373,301
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 988.4

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net sales	$ 4,186,497	$ 3,893,635	$ 2,884,603
Cost of sales	3,429,224	3,198,158	2,405,338
Gross profit	757,273	695,477	479,265
Selling, general and administrative	297,455	284,331	232,409
Research and development	166,614	117,206	82,017
Gain on sale of real estate	(108,109)	0	0
Total operating expenses	355,960	401,537	314,426
Operating income	401,313	293,940	164,839
Interest expense	83,839	79,668	81,407
Interest expense, related party	1,715	4,969	4,969
Other (income) expense, net	11,889	(5,854)	10,551
Total other expense, net	97,443	78,783	96,927
Income before taxes and equity in earnings of unconsolidated affiliate	303,870	215,157	67,912
Income tax expense	38,982	47,853	28,035
Income before equity in earnings of unconsolidated affiliate	264,888	167,304	39,877
Equity in earnings of J-Devices	0	0	14,016
Net income	264,888	167,304	53,893
Net income attributable to noncontrolling interests	(4,182)	(3,114)	(2,795)
Net income attributable to Amkor	$ 260,706	$ 164,190	$ 51,098
Net income attributable to Amkor per common share:
Basic (in dollars per share)	$ 1.09	$ 0.69	$ 0.22
Diluted (in dollars per share)	$ 1.09	$ 0.69	$ 0.22
Shares used in computing per common share amounts:
Basic (in shares)	238,937	237,416	236,850
Diluted (in shares)	239,651	238,034	237,170

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 264,888	$ 167,304	$ 53,893
Other comprehensive income (loss), net of tax:
Adjustments to unrealized components of defined benefit pension plans	5,165	2,563	1,100
Foreign currency translation	11,092	5,783	(146)
Equity interest in J-Devices' other comprehensive income (loss)	0	0	29,433
Total other comprehensive income (loss)	16,257	8,346	30,387
Comprehensive income	281,145	175,650	84,280
Comprehensive income attributable to noncontrolling interests	(4,182)	(3,114)	(2,795)
Comprehensive income attributable to Amkor	$ 276,963	$ 172,536	$ 81,485

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 596,364,000	$ 549,518,000
Restricted cash	2,000,000	2,000,000
Accounts receivable, net of allowances of $6,946 and $9,902, respectively	692,287,000	563,107,000
Inventories	326,492,000	267,990,000
Other current assets	33,727,000	27,081,000
Total current assets	1,650,870,000	1,409,696,000
Property, plant and equipment, net	2,695,065,000	2,564,648,000
Goodwill	25,036,000	24,122,000
Restricted cash	4,487,000	3,977,000
Other assets	146,051,000	89,643,000
Total assets	4,521,509,000	4,092,086,000
Current liabilities:
Short-term borrowings and current portion of long-term debt	123,848,000	35,192,000
Trade accounts payable	569,085,000	487,430,000
Capital expenditures payable	294,258,000	144,370,000
Accrued expenses	374,598,000	338,669,000
Total current liabilities	1,361,789,000	1,005,661,000
Long-term debt	1,240,581,000	1,364,638,000
Long-term debt, related party	0	75,000,000
Pension and severance obligations	182,216,000	166,701,000
Other non-current liabilities	46,144,000	76,682,000
Total liabilities	2,830,730,000	2,688,682,000
Commitments and contingencies (Note 17)
Amkor stockholders’ equity:
Preferred stock, $0.001 par value, 10,000 shares authorized, designated Series A, none issued	0	0
Common stock, $0.001 par value, 500,000 shares authorized, 285,129 and 284,479 shares issued, and 239,184 and 238,665 shares outstanding, respectively	285,000	284,000
Additional paid-in capital	1,903,357,000	1,895,089,000
Accumulated deficit	(42,851,000)	(303,557,000)
Accumulated other comprehensive income (loss)	22,519,000	6,262,000
Treasury stock, at cost, 45,945 and 45,814 shares, respectively	(215,982,000)	(214,490,000)
Total Amkor stockholders’ equity	1,667,328,000	1,383,588,000
Noncontrolling interests in subsidiaries	23,451,000	19,816,000
Total equity	1,690,779,000	1,403,404,000
Total liabilities and equity	$ 4,521,509,000	$ 4,092,086,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance	$ 6,946	$ 9,902
Preferred stock designated Series A, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock designated Series A, shares authorized (in shares)	10,000	10,000
Preferred stock designated Series A, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	500,000	500,000
Common stock, shares issued (in shares)	285,129	284,479
Common stock, shares outstanding (in shares)	239,184	238,665
Treasury stock, shares	45,945	45,814

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Total Amkor Stockholders' Equity	Common Stock	Additional Paid- In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Noncontrolling Interest in Subsidiaries
Balance at beginning of period, shares at Dec. 31, 2014			282,231,000
Balance at beginning of period, shares at Dec. 31, 2014							(45,604,000)
Balance at beginning of period at Dec. 31, 2014	$ 1,129,449	$ 1,114,748	$ 282	$ 1,878,810	$ (518,845)	$ (32,471)	$ (213,028)	$ 14,701
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	53,893
Net income attributable to Amkor	51,098	51,098			51,098
Net income attributable to noncontrolling interests	2,795							2,795
Total other comprehensive income (loss)	30,387	30,387				30,387
Treasury stock acquired through surrender of shares for tax withholding, shares							(115,000)
Treasury stock acquired through surrender of shares for tax withholding	(730)	(730)					$ (730)
Issuance of stock through share-based compensation plans, shares			493,000
Issuance of stock through share-based compensation plans	931	931	$ 1	930
Share-based compensation	3,852	3,852		3,852
Subsidiary dividends paid to noncontrolling interests	(246)							(246)
Balance at end of period, shares at Dec. 31, 2015			282,724,000
Balance at end of period, shares at Dec. 31, 2015							(45,719,000)
Balance at end of period at Dec. 31, 2015	1,217,536	1,200,286	$ 283	1,883,592	(467,747)	(2,084)	$ (213,758)	17,250
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	167,304
Net income attributable to Amkor	164,190	164,190			164,190
Net income attributable to noncontrolling interests	3,114							3,114
Total other comprehensive income (loss)	8,346	8,346				8,346
Treasury stock acquired through surrender of shares for tax withholding, shares							(95,000)
Treasury stock acquired through surrender of shares for tax withholding	(732)	(732)					$ (732)
Issuance of stock through share-based compensation plans, shares			1,755,000
Issuance of stock through share-based compensation plans	8,247	8,247	$ 1	8,246
Share-based compensation	3,251	3,251		3,251
Subsidiary dividends paid to noncontrolling interests	$ (548)							(548)
Balance at end of period, shares at Dec. 31, 2016	284,479		284,479,000
Balance at end of period, shares at Dec. 31, 2016	(45,814)						(45,814,000)
Balance at end of period at Dec. 31, 2016	$ 1,403,404	1,383,588	$ 284	1,895,089	(303,557)	6,262	$ (214,490)	19,816
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	264,888
Net income attributable to Amkor	260,706	260,706			260,706
Net income attributable to noncontrolling interests	4,182							4,182
Total other comprehensive income (loss)	16,257	16,257				16,257
Treasury stock acquired through surrender of shares for tax withholding, shares							(131,000)
Treasury stock acquired through surrender of shares for tax withholding	(1,492)	(1,492)					$ (1,492)
Issuance of stock through share-based compensation plans, shares			650,000
Issuance of stock through share-based compensation plans	3,124	3,124	$ 1	3,123
Share-based compensation	5,145	5,145		5,145
Subsidiary dividends paid to noncontrolling interests	$ (547)							(547)
Balance at end of period, shares at Dec. 31, 2017	285,129		285,129,000
Balance at end of period, shares at Dec. 31, 2017	(45,945)						(45,945,000)
Balance at end of period at Dec. 31, 2017	$ 1,690,779	$ 1,667,328	$ 285	$ 1,903,357	$ (42,851)	$ 22,519	$ (215,982)	$ 23,451

Consolidated Statements of Cash

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	$ 264,888	$ 167,304	$ 53,893
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	581,940	555,186	494,200
Gain on sale of real estate	(108,109)	0	0
Amortization of deferred debt issuance costs and premiums	1,235	1,403	1,665
Deferred income taxes	(42,998)	(1,746)	(697)
Equity in earnings of unconsolidated affiliate	0	0	(14,016)
Loss on debt retirement	4,835	0	9,560
Loss (gain) on disposal of fixed assets, net	(2,648)	1,390	1,190
Share-based compensation	5,145	3,251	3,852
Loss from acquisition of J-Devices	0	0	13,501
Proceeds from insurance recovery for property, plant and equipment	0	(15,166)	0
Other, net	(8,143)	2,858	4,014
Changes in assets and liabilities, net of acquisitions:
Accounts receivable	(118,353)	(29,126)	122,840
Inventories	(54,195)	(28,397)	27,677
Other current assets	(2,473)	1,124	(3,309)
Other assets	(458)	1,037	333
Trade accounts payable	67,574	48,581	(48,368)
Accrued expenses	35,525	56,465	(42,042)
Pension and severance obligations	23,881	1,625	(7,321)
Other non-current liabilities	(29,379)	(36,387)	(31,997)
Net cash provided by operating activities	618,267	729,402	584,975
Cash flows from investing activities:
Payments for property, plant and equipment	(550,943)	(650,038)	(537,975)
Proceeds from sale of property, plant and equipment	141,530	45,635	6,945
Proceeds from insurance recovery for property, plant and equipment	0	15,166	0
Acquisition of business, net of cash acquired	(43,771)	0	22,577
Investment in J-Devices	0	0	(12,908)
Disposition of business to J-Devices, net of cash transferred	0	0	8,355
Other investing activities	(1,648)	(190)	(1,984)
Net cash used in investing activities	(454,832)	(589,427)	(514,990)
Cash flows from financing activities:
Proceeds from revolving credit facilities	75,000	125,000	290,000
Payments of revolving credit facilities	0	(255,000)	(150,000)
Proceeds from short-term debt	77,781	49,131	0
Payments of short-term debt	(70,236)	(49,500)	0
Proceeds from issuance of long-term debt	223,976	46,000	400,000
Payments of long-term debt	(405,269)	(32,078)	(537,030)
Payments of long-term debt, related party	(17,837)	0	0
Payments of capital lease obligations	(5,340)	(2,543)	0
Payment of deferred consideration for purchase of facility	(3,890)	0	0
Proceeds from issuance of stock through share-based compensation plans	3,124	8,247	931
Other financing activities	(2,195)	(1,436)	(1,288)
Net cash (used in) provided by financing activities	(124,886)	(112,179)	2,613
Effect of exchange rate fluctuations on cash, cash equivalents and restricted cash	8,807	351	0
Net increase in cash, cash equivalents and restricted cash	47,356	28,147	72,598
Cash, cash equivalents and restricted cash, beginning of period	555,495	527,348	454,750
Cash, cash equivalents and restricted cash, end of period	602,851	555,495	527,348
Cash paid during the period for:
Interest	83,808	86,777	96,227
Income taxes	61,878	32,174	35,084
Non-cash investing and financing activities:
Property, plant and equipment included in capital expenditures payable	294,912	146,080	242,980
Equipment acquired through capital lease	$ 929	$ 6,358	$ 0

Description of Business and Sum

Description of Business and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Summary of Significant Accounting Policies	Description of Business and Summary of Significant Accounting Policies Description of Business Amkor is one of the world’s leading providers of outsourced semiconductor packaging and test services. Amkor pioneered the outsourcing of semiconductor packaging and test services through a predecessor corporation in 1968, and over the years we have built a leading position by: • Designing and developing innovative packaging and test technologies; • Offering a broad portfolio of cost-effective solutions and services; • Focusing on strategic end markets that offer solid growth potential; • Cultivating long-standing relationships with our customers, which include many of the world’s leading semiconductor companies; • Collaborating with customers, original equipment manufacturers ("OEMs") and equipment and material suppliers; • Developing a competitive cost structure with disciplined capital investment; • Building expertise in high-volume manufacturing processes and developing a reputation for high quality and solid execution and • Providing a geographically diverse operating base, with research and development, engineering support and production capabilities at various facilities throughout China, Japan, Korea, Malaysia, the Philippines, Portugal and Taiwan. Basis of Presentation Our Consolidated Financial Statements include the accounts of Amkor Technology, Inc. and our subsidiaries (“Amkor”). Our Consolidated Financial Statements reflect the elimination of all significant inter-company accounts and transactions. On December 30, 2015 , we increased our investment in J-Devices to 100% ( Note 3 ). As a result, our accounting for J-Devices changed from the equity method to the consolidation method effective December 30, 2015. The operating results of J-Devices were consolidated beginning in 2016. On May 22, 2017, we completed the purchase of Nanium, S.A. ("Nanium"). Nanium's financial results have been included in our Consolidated Financial Statements from the date of acquisition ( Note 3 ). Our investments in variable interest entities in which we are the primary beneficiary are consolidated. We reflect the remaining portion of variable interest entities and foreign subsidiaries that are not wholly owned as noncontrolling interests. The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, we evaluate our estimates, including those related to acquisitions, revenue recognition, income taxes, inventory, long lived assets and contingencies. These estimates are based on management’s best knowledge of current events, historical experience, actions that we may undertake in the future and on various other assumptions that are believed to be reasonable under the circumstances. As a result, actual results could differ materially from these estimates and assumptions. Certain prior year amounts have been reclassified to conform to current year presentation. Consolidation of Variable Interest Entities We have variable interests in certain Philippine realty corporations in which we have a 40% ownership. We lease land and buildings in the Philippines from these entities and we are the primary beneficiary of these arrangements. As of December 31, 2017 , the combined book value of the assets and liabilities associated with these Philippine realty corporations included in our Consolidated Balance Sheet was $16.9 million and $0.4 million , respectively. The impact of consolidating these variable interest entities on our Consolidated Statements of Income was not significant, and other than our lease payments, we have not provided any significant assistance or other financial support to these variable interest entities for the years ended December 31, 2017 , 2016 or 2015 . The creditors of the Philippine realty corporations have no recourse to our general credit. Foreign Currency Translation The U.S. dollar is the functional currency of our subsidiaries other than J-Devices, and the foreign currency asset and liability amounts at these subsidiaries are remeasured into U.S. dollars at end-of-period exchange rates, except for nonmonetary items which are remeasured at historical rates. Foreign currency income and expenses are remeasured at daily exchange rates, except for expenses related to balance sheet amounts which are remeasured at historical exchange rates. Exchange gains and losses arising from remeasurement of foreign currency-denominated monetary assets and liabilities are included in other (income) expense, net in the period in which they occur. The Japanese Yen is the functional currency of J-Devices. The asset and liability amounts of J-Devices are translated into U.S. dollars at end-of-period exchange rates. Income and expenses are translated into U.S. dollars at average exchange rates in effect during the period. The resulting translation adjustments are reported as a component of accumulated other comprehensive income in the stockholders’ equity section of the balance sheet. Assets and liabilities denominated in a currency other than the functional currency are remeasured into the functional currency prior to translation into U.S. dollars, and the resulting transaction exchange gains or losses are included in other expense (income) in the period in which they occur. Risks and Concentrations The semiconductor industry is characterized by rapid technological change, competitive pricing pressures and cyclical market patterns. Our financial results are affected by a wide variety of factors, including general economic conditions worldwide, economic conditions specific to the semiconductor industry, the timely implementation of new package and test technologies, the ability to safeguard patents and intellectual property in a rapidly evolving market and reliance on materials and equipment suppliers. In addition, the semiconductor market has historically been cyclical and subject to significant economic downturns at various times. Our profitability and ability to generate cash from operations is principally dependent upon demand for semiconductors, the utilization of our capacity, semiconductor package mix, the average selling price of our services, our ability to manage our capital expenditures and our ability to control our costs including labor, material, overhead and financing costs. A significant portion of our revenues is concentrated with a small group of customers ( Note 18 ). The loss of a significant customer, a business combination among customers, a reduction in orders or decrease in price from a significant customer or disruption in any of our significant strategic partnerships or other commercial arrangements could have a material adverse effect on our business, liquidity, results of operations, financial condition and cash flows. Financial instruments, for which we are subject to credit risk, consist principally of accounts receivable and cash and cash equivalents. With respect to accounts receivable, we mitigate our credit risk by selling primarily to well-established companies, performing ongoing credit evaluations and making frequent contact with customers. In addition, we may utilize non-recourse factoring to mitigate credit risk when considered appropriate. We have historically mitigated our credit risk with respect to cash and cash equivalents through diversification of our holdings into various high quality money market funds and bank deposit accounts. At December 31, 2017 , our cash and cash equivalents were maintained in various U.S. and foreign bank operating and time deposit accounts and invested in U.S. money market funds. Contingencies and Litigation We may be subject to certain legal proceedings, lawsuits and other claims, as discussed in Note 17 . We accrue for a loss contingency, including legal proceedings, lawsuits, pending claims and other legal matters, when we conclude that the likelihood of a loss is probable and the amount of the loss can be reasonably estimated. When the reasonable estimate of the loss is within a range of amounts, and no amount in the range constitutes a better estimate than any other amount, we accrue for the amount at the low end of the range. We adjust our accruals from time to time as we receive additional information, but the loss we incur may be significantly greater than or less than the amount we have accrued. We disclose loss contingencies if we believe they are material and there is at least a reasonable possibility that a loss has been incurred. Attorney fees related to legal matters are expensed as incurred. Cash and Cash Equivalents We consider all highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Our cash and cash equivalents are maintained in various U.S. and foreign bank operating and time deposit accounts and invested in U.S. money market funds. Restricted Cash Restricted cash, current, consists of short-term cash equivalents used to collateralize our daily banking services. Restricted cash, non-current, mainly consists of collateral to fulfill foreign trade compliance requirements. Inventories Inventories are stated at the lower of cost and net realizable value. Cost is principally determined by standard cost or the weighted moving average method, both of which approximate actual cost. We review and set our standard costs as needed, but at a minimum on an annual basis. We reduce the carrying value of our inventories for the cost of inventory we estimate is excess and obsolete based on the age of our inventories. When a determination is made that the inventory will not be utilized in production or is not saleable, it is written-off. Other Current Assets Other current assets consist principally of prepaid assets and an investment in government securities by a foreign subsidiary to satisfy local regulatory requirements, which is recorded at amortized cost. Property, Plant and Equipment Property, plant and equipment are stated at cost. Depreciation is calculated by the straight-line method over the estimated useful lives of depreciable assets which are as follows: Land use rights 50 to 90 years Buildings and improvements 10 to 40 years Machinery and equipment 2 to 7 years Software and computer equipment 3 to 5 years Furniture, fixtures and other equipment 4 to 10 years Cost and accumulated depreciation for property retired or disposed of are removed from the accounts, and any resulting gain or loss is included in earnings. Expenditures for maintenance and repairs are charged to expense as incurred. We review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. Recoverability of a long-lived asset group to be held and used in operations is measured by a comparison of the carrying amount to the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the asset group. If such asset group is considered to be impaired, the impairment loss is measured as the amount by which the carrying amount of the asset group exceeds its fair value. Long-lived assets to be disposed of are carried at the lower of cost or fair value less the costs of disposal. Goodwill Goodwill is recorded when the cost of an acquisition exceeds the fair value of the net tangible and identifiable intangible assets acquired. We review goodwill for impairment annually during the fourth quarter of each year and whenever events or changes in circumstances indicate that an impairment may exist. Impairment losses are recorded when the carrying amount of the reporting unit exceeds its fair value. Other Assets Other assets consist principally of deferred tax assets and refundable security deposits. Fair Value Measurements We apply fair value accounting for assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring or nonrecurring basis. We define fair value as the price that would be received from selling an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. See Note 16 for further discussion of fair value measurements. Revenue Recognition We recognize revenue from our packaging and test services, net of value-added or other similar taxes, when there is evidence of an arrangement, delivery has occurred or services have been rendered, fees are fixed or determinable and collectibility is reasonably assured. Generally, these criteria are met and revenue is recognized upon shipment or, in some cases, customer acceptance. If the revenue recognition criteria are not met, we defer the revenue. Deferred revenue generally results from two types of transactions: contractual invoicing at interim points in the packaging and test process prior to shipment of the finished product and customer advances for supply agreements with customers where we commit capacity in exchange for customer prepayment of services. These prepayments are deferred and recorded as customer advances within accrued expenses and other non-current liabilities. We generally do not take ownership of customer-supplied semiconductor wafers. Title and risk of loss remains with the customer for these materials at all times. Accordingly, the cost of the customer-supplied materials is not included in our Consolidated Financial Statements. An allowance for sales credits is recorded as a reduction to sales and accounts receivable during the period of sale such that accounts receivable is reported at its estimated net realizable value. The allowance for sales credits is an estimate of the future credits we will issue for billing adjustments primarily for invoicing corrections and miscellaneous customer claims and is estimated based upon recent credit issuance, historical experience and specific identification of known or expected sales credits at the end of the reporting period. Additionally, provisions are made for doubtful accounts when there is doubt as to the collectibility of accounts receivable. The allowance for doubtful accounts is recorded as bad debt expense and is classified as selling, general and administrative expense. The allowance for doubtful accounts is based upon specific identification of doubtful accounts considering the age of the receivable balance, the customer’s historical payment history and current credit worthiness as well as specific identification of any known or expected collectibility issues. Historically, our allowance for doubtful accounts has been immaterial. Shipping and Handling Fees and Costs Amounts billed to customers for shipping and handling are presented in net sales. Costs incurred for shipping and handling are included in cost of sales. Research and Development Costs Research and development expenses include costs attributable to the conduct of research and development programs primarily related to the development of new package designs or technologies and improving the efficiency and capabilities of our existing production processes. Such costs include salaries, payroll taxes, employee benefit costs, materials, supplies, depreciation and maintenance of research equipment, services provided by outside contractors and the allocable portions of facility costs such as rent, utilities, insurance, repairs and maintenance, depreciation and general support services. All costs associated with research and development are expensed as incurred. Income Taxes Income taxes are accounted for using the asset and liability method. Under this method, deferred income tax assets and liabilities are recognized for the future tax consequences attributable to temporary differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis as well as for net operating loss and tax credit carryforwards. Deferred income tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which these temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is provided for those deferred tax assets for which it is more likely than not that the related tax benefits will not be realized. We monitor on an ongoing basis our ability to utilize our deferred tax assets and whether there is a need for a related valuation allowance. In evaluating our ability to recover our deferred tax assets in the jurisdictions from which they arise, we consider all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax-planning strategies and results of recent operations. For most of our U.S. and foreign deferred tax assets, we consider it more likely than not that we will have sufficient taxable income to allow us to realize these deferred tax assets. However, in the event taxable income falls short of current expectations, we may need to establish a valuation allowance against such deferred tax assets. ASC 740, Accounting for Income Taxes, requires companies to recognize the effect of tax law changes in the period of enactment even though the effective date for most provisions is for tax years beginning after December 31, 2017. Given the significance of the Tax Act, the SEC staff issued Staff Accounting Bulletin No. 118, which allows registrants to record provisional amounts during a one year “measurement period” similar to that used when accounting for business combinations. However, the measurement period is deemed to have ended earlier when the registrant has obtained, prepared and analyzed the information necessary to finalize its accounting. During the measurement period, impacts of the law are expected to be recorded at the time a reasonable estimate for all or a portion of the effects can be made, and provisional amounts can be recognized and adjusted as information becomes available, prepared or analyzed. We have reported provisional amounts for the income tax effects of the Tax Act for which the accounting is incomplete but a reasonable estimate could be determined. There were no specific impacts of the Tax Act that could not be reasonably estimated. Our estimate of the impact of the Tax Act may be adjusted throughout the allowable measurement period as we collect additional information, prepare and analyze the information and evaluate any regulatory guidance or clarifications. Our review is expected to include: • One-time transition tax: Further information is required to substantiate the underlying data supporting foreign earnings and profits, foreign tax credits, and amounts held in liquid and illiquid assets at various measurement dates. Changes to our provisional estimates and further analysis could impact our judgments, elections and assertions. • Remeasurement of deferred tax assets and liabilities: Further analysis is required to calculate the impact on the related account balances including the impact of complex new provisions which include the Base Erosion Anti-abuse Tax and Global Intangible Low-Taxed Income (“GILTI”), designed to subject certain foreign earnings to U.S. tax. • Valuation allowances: We have assessed whether valuation allowance analyses for deferred tax assets are affected by various aspects of the Tax Act (for example one-time transition tax, GILTI, new categories of foreign tax credits). Since we have recorded provisional amounts related to the provisions of the Tax Act, any corresponding determination of the need for a change in a valuation allowance is also provisional. We recognize in our Consolidated Financial Statements the impact of an income tax position, if that position is more likely than not of being sustained on audit, based on the technical merits of the position. Related interest and penalties are classified as income taxes in the financial statements. See Note 6 for more information regarding unrecognized income tax benefits.

New Accounting Standards

New Accounting Standards	12 Months Ended
	Dec. 31, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Standards	New Accounting Standards Recently Adopted Standards In July 2015, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2015-11, Inventory - Simplifying the Measurement of Inventory (Topic 330) . ASU 2015-11 requires inventory to be subsequently measured using the lower of cost and net realizable value, thereby eliminating the market value approach. Net realizable value is defined as the “estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation.” ASU 2015-11 is effective for reporting periods beginning after December 15, 2016 and is applied prospectively. We adopted ASU 2015-11 at January 1, 2017. The adoption of ASU 2015-11 did not have a significant impact on our financial statements or disclosure. In January 2017, the FASB issued ASU 2017-04, Intangible - Goodwill and Other (Topic 350) - Simplifying the Test for Goodwill Impairment . ASU 2017-04 simplifies the goodwill impairment test by eliminating the second step of the current two-step impairment test. ASU 2017-04 is effective for interim and annual goodwill impairment tests in fiscal years beginning after December 15, 2019 and is applied prospectively. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. We adopted ASU 2017-04 at January 1, 2017. The adoption of ASU 2017-04 did not have a significant impact on our financial statements or disclosure. Recently Issued Standards In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) . ASU 2014-09 is based on the principle that revenue is recognized to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This ASU also requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers, including significant judgments and changes in judgments. ASU 2014-09 permits the use of either full retrospective or modified retrospective methods of adoption. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which defers the effective date by one year to December 15, 2017, for interim and annual reporting periods beginning after that date . In March, April, May and December 2016, the FASB issued ASU 2016-08 , ASU 2016-10, ASU 2016-12 and ASU 2016-20, respectively, which provide supplemental guidance and clarification to ASU 2014-09. In September 2017, the FASB issued ASU 2017-13, which provides supplemental guidance and clarification to ASU 2014-09. The new standard will result in a change to the timing of revenue recognition, whereby revenue will be recognized "over time" as services are performed rather than at a "point in time", generally upon shipment. The new standard will also result in an increase in accounts receivables, net and a related decrease in inventories, deferred revenues and accumulated deficit. We will adopt the standard using the full retrospective method to adjust each prior reporting period presented. We are in the process of finalizing the impact that this new standard will have on our consolidated financial statements and disclosure; however, we expect the following impacts to our reported results: For the Year Ended December 31, 2017 As Reported New Revenue Standard Adjustment (Estimate) As Adjusted (Estimate) (In thousands, except per share data) Income Statement: Net sales $ 4,186,497 $ 24,000 $ 4,210,497 Cost of sales 3,429,224 17,000 3,446,224 Net income 264,888 5,000 269,888 Net income attributable to Amkor per common share: Basic 1.09 0.02 1.11 Diluted 1.09 0.02 1.11 For the Year Ended December 31, 2016 As Reported New Revenue As Adjusted (In thousands, except per share data) Income Statement: Net sales $ 3,893,635 $ 36,000 $ 3,929,635 Cost of sales 3,198,158 21,000 3,219,158 Net income 167,304 11,000 178,304 Net income attributable to Amkor per common share: Basic 0.69 0.05 0.74 Diluted 0.69 0.04 0.73 December 31, 2017 As New Revenue As Adjusted (In thousands) Balance Sheet: Accounts receivable, net $ 692,287 $ 106,000 $ 798,287 Inventories 326,492 (113,000 ) 213,492 Accrued expenses 374,598 (48,000 ) 326,598 Accumulated deficit (42,851 ) 31,000 (11,851 ) In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . ASU 2016-02 requires a dual approach for lessee accounting under which a lessee would account for leases as finance leases or operating leases. Both finance leases and operating leases will result in the lessee recognizing a right-of-use asset and a corresponding lease liability. For finance leases the lessee would recognize interest expense and amortization of the right-of-use asset, and for operating leases the lessee would recognize a straight-line lease expense. ASU 2016-02 is effective for reporting periods beginning after December 15, 2018 using a modified retrospective approach. Early adoption is permitted. In September 2017 and January 2018, the FASB issued ASU 2017-13 and ASU 2018-01, respectively, which provide supplemental guidance and clarification to ASU 2016-02. We are currently evaluating the impact that this guidance may have on our financial statements and disclosure. In March 2017, the FASB issued ASU 2017-07, Compensation – Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . ASU 2017-07 requires that the service cost component of net periodic pension costs be presented in the same line item as other compensation costs and all other components of net periodic pension costs to be presented in the statement of income as nonoperating expenses. ASU 2017-07 is effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods. We will use the amounts previously disclosed within the prior year financial statements as a practical expedient for retrospective presentation within the consolidated statements of income. ASU 2017-07 will not have a material impact to our financial statements upon adoption. In February 2018, the FASB issued ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. ASU 2018-02 allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Act. ASU 2018-02 is effective for fiscal years, including interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. Adoption of this ASU should be applied either in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Act is recognized. We are currently evaluating the impact that this guidance may have on our financial statements and disclosure.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisitions	Acquisitions Acquisition of Nanium On May 22, 2017, we completed the purchase of 100% of the shares of Nanium, a provider of wafer-level fan-out semiconductor packaging solutions. We allocated the purchase price to the assets acquired and liabilities assumed based on their estimated fair values on the date of acquisition. We did not record goodwill as a result of the acquisition. Step-acquisition of J-Devices On December 30, 2015, through the exercise of additional options, we increased our ownership interest in J-Devices from 65.7% to 100% for a purchase price of $105.4 million . As a result, our accounting for J-Devices changed from the equity method to the consolidation method effective December 30, 2015. The operating results of J-Devices were consolidated beginning in 2016. The acquisition of the remaining interest expands our presence in Japan and our business worldwide by capitalizing on our leadership position in the automotive market. Since there were no material transactions from December 30, 2015 to December 31, 2015, and for the convenience of reporting the acquisition for accounting purposes, December 31, 2015 was designated as the acquisition date. The following table summarizes the consideration transferred to acquire J-Devices and the amounts of identifiable assets acquired and liabilities assumed at the acquisition date: (In thousands) Fair value of consideration transferred: Cash $ 105,391 Fair value of our previously held equity interest in J-Devices 160,087 Total $ 265,478 Recognized amounts of identifiable assets acquired and liabilities assumed: Cash $ 127,968 Accounts receivable 180,177 Inventory 42,502 Other current assets 2,363 Property, plant and equipment 230,319 Other assets 9,268 Short-term borrowings and current portion of long-term debt (36,770 ) Other current liabilities (251,405 ) Long-term debt (18,885 ) Pension obligations (22,250 ) Other non-current liabilities (21,218 ) Total identifiable net assets 242,069 Goodwill 23,409 Total $ 265,478 The goodwill is attributable to the workforce of J-Devices, as well as cost savings and synergies expected from combining the operations of J-Devices. It is not deductible for tax purposes. As a result of obtaining control over J-Devices, our previously held equity interest of 65.7% was remeasured to fair value, resulting in a gain of $16.1 million . Additionally, our previously held equity interest in J-Devices' accumulated foreign currency translation adjustments was released upon consolidation of J-Devices, resulting in a loss of $29.6 million . The combined net loss of $13.5 million was recognized in other (income) expense, net ( Note 5 ) in our Consolidated Financial Statements. The fair value of our previously held equity interest in J-Devices was estimated by applying an income approach using the discounted cash flow method. The fair value measurement is based on significant inputs not observable in the market and thus represents a Level 3 fair value measurement. Key assumptions include our estimates of J-Devices’ financial projections, a terminal value based on its expected long-term growth rate and a discount rate based on the weighted-average cost of capital of comparable companies. The following unaudited pro forma consolidated results of operations have been prepared as if the acquisition of J-Devices had occurred on January 1, 2014. The pro forma results include adjustments related to alignment to our accounting policies, the effect of fair value adjustments on property, plant and equipment and the related income tax effect. We also eliminated inter-company activity between the parties in the consolidated results. The pro forma results include the activities that are nonrecurring and not representative of future activities, including the gain of $16.2 million from reversal of a deferred tax asset valuation allowance and the gain of $12.6 million from release of accumulated foreign currency translation adjustments associated with merging our subsidiary into J-Devices in 2014, offset by the loss on acquisition of J-Devices of $13.5 million in 2014. This pro forma data is presented for informational purposes only and does not purport to be indicative of the results of future operations or of the results that would have occurred had the 2015 acquisition taken place on January 1, 2014. The pro forma information does not include any potential revenue enhancements, cost synergies or other operating efficiencies that could result from the acquisition. For the Year Ended December 31 2015 2014 (unaudited) (unaudited) (In thousands, except per share data) Net sales $ 3,696,495 $ 4,051,076 Net income 88,190 153,049 Net income attributable to Amkor 85,394 149,548 Basic earnings per share 0.36 0.65 Diluted earnings per share 0.36 0.63

Share-Based Compensation Plans

Share-Based Compensation Plans	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation Plans	Share-Based Compensation Plans Our share-based compensation is measured at fair value and expensed over the service period (generally the vesting period). The amount of compensation expense to be recognized is adjusted for an estimated forfeiture rate which is based on historical data. For the years ended December 31, 2017 , 2016 and 2015 , we recognized share-based compensation attributable to stock options and restricted shares of $5.1 million , $3.3 million and $3.9 million , respectively, primarily in selling, general and administrative expenses. The corresponding deferred income tax benefits for stock options or restricted shares is $2.4 million for 2017 and zero for 2016 and 2015. Equity Incentive Plan Amended and Restated 2007 Equity Incentive Plan. The Amended and Restated 2007 Equity Incentive Plan, (the “2007 Plan”) provides for the grant of the following types of incentive awards: (i) stock options, (ii) restricted stock, (iii) restricted stock units, (iv) stock appreciation rights, (v) performance units and performance shares and (vi) other stock or cash awards. Those eligible for awards include employees, directors and consultants who provide services to Amkor and its subsidiaries. The 2007 Plan is effective through 2027 and can be terminated at the discretion of the Board of Directors. There were originally 17.0 million shares of our common stock reserved for issuance under the 2007 Plan and at December 31, 2017 there were 8.0 million shares available for grant. Stock options Stock options are generally granted with an exercise price equal to the market price of the stock at the date of grant. Substantially all of the options granted are exercisable pursuant to a one to four year vesting schedule and the term of the options granted is no longer than ten years. Upon option exercise, we may issue new shares of common or treasury stock. In order to calculate the fair value of stock options at the date of grant, we use the Black-Scholes option pricing model. Expected volatilities are based on historical performance of our stock. We also use historical data to estimate the timing and amount of option exercises and forfeitures within the valuation model. The expected term of the options is based on evaluations of historical and expected future employee exercise behavior and represents the period of time that options granted are expected to be outstanding. The risk-free interest rate for periods within the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant. The following table summarizes our stock option activity for the year ended December 31, 2017 : Number of Shares (In thousands) Weighted-Average Exercise Price per Share Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (In thousands) Outstanding at December 31, 2016 2,443 $ 6.93 Granted 2,900 9.97 Exercised (469) 6.66 Forfeited or expired (122) 5.12 Outstanding at December 31, 2017 4,752 $ 8.86 7.51 $ 6,403 Fully vested at December 31, 2017 and expected to vest thereafter 4,632 $ 8.83 7.46 $ 6,369 Exercisable at December 31, 2017 1,733 $ 7.17 4.75 $ 5,455 The following assumptions were used to calculate the weighted-average fair values of the options granted: For the Year Ended December 31, 2017 2016 2015 Expected life (in years) 5.7 6.5 5.8 Risk-free interest rate 1.9 % 1.5 % 1.8 % Volatility 43 % 48 % 45 % Dividend yield — — — Weighted-average grant date fair value per option granted $ 4.24 $ 2.89 $ 3.14 Total unrecognized compensation expense from stock options was $9.6 million as of December 31, 2017 , which is expected to be recognized over a weighted-average period of approximately 3.0 years beginning January 1, 2017. Restricted Shares We grant restricted shares to directors and employees under the 2007 Plan. Restricted shares granted to directors vest on the earlier of the one year anniversary of the grant date or the date of the next annual meeting of stockholders. All other restricted shares vest ratably over four years, with 6.25% of the shares vesting in equal quarterly installments such that 100% of the shares will become vested on the fourth anniversary of the award, subject to the recipient’s continued employment with us on the applicable vesting dates. In addition, provided that the restricted shares have not been forfeited earlier, for certain grants, the restricted shares will vest upon the recipient’s death or disability, or upon a change in control of Amkor. The value of the restricted shares is determined based on the fair market value of the underlying shares on the date of the grant and is recognized ratably over the vesting period. Upon vesting of restricted stock awards, we may issue new shares of common or treasury stock. The following table summarizes our restricted share activity for the year ended December 31, 2017 : Number of Shares (In thousands) Weighted- average Grant Date Fair Value (Per Share) Nonvested at December 31, 2016 145 $ 5.02 Awards granted 224 10.06 Awards vested (181 ) 5.93 Awards forfeited — — Nonvested at December 31, 2017 188 10.15 Total unrecognized compensation cost from restricted shares was $1.5 million as of December 31, 2017 , which is expected to be recognized over a weighted-average period of approximately 2.8 years beginning January 1, 2017.

Other Income and Expense

Other Income and Expense	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Other Income and Expense	Other Income and Expense Other income and expense consists of the following: For the Year Ended December 31, 2017 2016 2015 (In thousands) Interest income $ (3,215 ) $ (1,326 ) $ (2,539 ) Foreign currency (gain) loss, net 11,823 (3,592 ) (7,849 ) Loss on debt retirement 4,835 — 9,560 Loss from acquisition of J-Devices (Note 3) — — 13,501 Other (income) expense, net (1,554 ) (936 ) (2,122 ) Total other (income) expense, net $ 11,889 $ (5,854 ) $ 10,551

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes On December 22, 2017, the Tax Act was signed into law. The Tax Act reduced the corporate tax rate from 35% to 21%, included a one-time transition tax on unremitted foreign earnings and profits applicable for our fiscal year ended December 31, 2017 and limited tax deductions for interest expense for periods beginning January 1, 2018 which caused a release of valuation allowance. In 2017, we recognized a net benefit for the impact of the Tax Act with components as follows: (In thousands) One-time transition tax before credits $ 162,750 Tax credits (128,395 ) Remeasure deferred tax assets 36,794 Release valuation allowance (112,703 ) Net impact of the Tax Act $ (41,554 ) In accordance with SEC staff issued Staff Accounting Bulletin No. 118, we have not finalized our accounting and have made a provisional estimate of the impacts of the Tax Act. (See Note 1). Geographic sources of income (loss) before taxes and equity in earnings of unconsolidated affiliate are as follows: For the Year Ended December 31, 2017 2016 2015 (In thousands) United States $ 14,935 $ (12,385 ) $ (39,684 ) Foreign 288,935 227,542 107,596 Income before taxes and equity in earnings of unconsolidated affiliate $ 303,870 $ 215,157 $ 67,912 The provision for income taxes includes current federal, state and foreign taxes payable and those deferred because of temporary differences between the financial statement and the tax bases of assets and liabilities. The components of the provision (benefit) for income taxes are as follows: For the Year Ended December 31 2017 2016 2015 (In thousands) Current: Federal $ — $ — $ — State 11 22 11 Foreign 81,969 49,577 28,721 81,980 49,599 28,732 Deferred: Federal (36,943 ) — — State (4,611 ) — — Foreign (1,444 ) (1,746 ) (697 ) (42,998 ) (1,746 ) (697 ) Income tax expense $ 38,982 $ 47,853 $ 28,035 The reconciliation between the U.S. federal statutory income tax rate of 35% and our income tax expense is as follows: For the Year Ended December 31 2017 2016 2015 (In thousands) U.S. federal tax at 35% $ 106,354 $ 75,305 $ 23,769 State taxes, net of federal benefit 2,193 836 2,622 Foreign income taxed at different rates (51,412 ) (17,907 ) (11,756 ) Foreign exchange (loss) gain 29,756 (1,127 ) (5,680 ) Change in valuation allowance (4,703 ) (7,362 ) 18,259 Adjustments related to prior years 3,329 (2,648 ) (912 ) U.S. tax reform (the Tax Act) (41,554 ) — — Income tax credits generated (7,296 ) (40,301 ) (1,919 ) Repatriation of foreign earnings and profits 719 25,604 91 Expiration of net operating losses and credits 166 15,092 74 Non-deductible loss on acquisition of J-Devices (Note 3) — — 4,725 Other 1,430 361 (1,238 ) Income tax expense $ 38,982 $ 47,853 $ 28,035 The change in valuation allowance, excluding the impact of the Tax Act, for 2017, 2016 and 2015 is primarily the result of changes in net operating loss and tax credit carryforwards for which no tax expense or benefit has been recognized. The benefit of foreign income taxed at different rates has increased as foreign income before tax has increased. In 2016, we recognized taxable income and associated foreign income tax credits from the repatriation of foreign earnings and profits in connection with the merger of our Japanese subsidiaries. In 2015, we recognized a loss in connection with our increased ownership interest in J-Devices which is not deductible for income tax purposes. The following is a summary of the components of our deferred tax assets and liabilities: December 31, 2017 2016 (In thousands) Deferred tax assets: Net operating loss carryforwards $ 53,130 $ 111,899 Income tax credits 23,998 41,900 Property, plant and equipment 35,479 21,860 Accrued liabilities 68,091 68,563 Receivable 32,719 — Unrealized foreign exchange loss 1,924 531 Other 12,682 14,583 Total deferred tax assets 228,023 259,336 Valuation allowance (83,338 ) (165,367 ) Total deferred tax assets net of valuation allowance 144,685 93,969 Deferred tax liabilities: Property, plant and equipment 15,754 20,407 Deferred gain 939 2,655 Unrealized foreign exchange gain 8,383 990 Other 4,566 4,836 Total deferred tax liabilities 29,642 28,888 Net deferred tax assets $ 115,043 $ 65,081 Recognized as: Other assets 117,608 66,831 Other non-current liabilities (2,565 ) (1,750 ) Total $ 115,043 $ 65,081 Valuation allowance against deferred tax assets consist of the following: December 31, 2017 2016 (In thousands) Valuation allowance: U.S. $ 43,719 $ 164,479 Portugal 39,009 — Other 610 888 Total valuation allowance $ 83,338 $ 165,367 U.S. deferred tax assets and liabilities were remeasured down to the new U.S. federal tax rate of 21% as a result of the Tax Act. In connection with our acquisition of Nanium, we acquired a receivable which resulted in the creation of a deferred tax asset. The decrease in our valuation allowance included the reversal of the valuation allowance against most of our U.S. deferred tax assets in connection with the Tax Act offset by the valuation allowance against the deferred tax assets of our Portuguese deferred tax assets, acquired in 2017. As a result of certain capital investments, export commitments and employment levels, income from operations in Korea, Malaysia, the Philippines, Singapore and Taiwan was subject to reduced income tax rates and, in some cases, was exempt from income taxes. We recognized $6.2 million , $5.6 million and $3.3 million in tax benefits as a result of the tax holidays in 2017 , 2016 and 2015 , respectively. The benefit of the tax holidays on diluted earnings per share was approximately $0.03 , $0.02 and $0.01 for 2017 , 2016 and 2015 , respectively. Our net operating loss carryforwards (“NOL’s”) are as follows: December 31, 2017 2016 Expiration (In thousands) U.S. Federal NOL’s $ 220,445 $ 292,715 2021-2037 U.S. State NOL’s 121,095 138,218 2018-2036 Foreign NOL’s 2,967 3,378 2018-2025 We monitor on an ongoing basis our ability to utilize our deferred tax assets and whether there is a need for a related valuation allowance. In evaluating our ability to recover our deferred tax assets in the jurisdictions from which they arise, we consider all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax-planning strategies and results of recent operations. For most of our U.S. and foreign deferred tax assets, we consider it more likely than not that we will have sufficient taxable income to allow us to realize these deferred tax assets. In prior years, the deferred tax assets along with the U.S. federal and state net operating losses available for carryforward have been fully reserved with valuation allowances. During the fourth quarter of 2017, we determined it was more likely than not that we will have sufficient taxable income to allow us to realize most of our U.S. deferred tax assets, including a substantial portion of our U.S. net operating loss carryforward. Our evaluation considered, among other factors, limitations on the deductibility of interest expense in connection with the Tax Act. At December 31, 2017, a portion of our U.S. federal net operating loss carryforward continues to be reserved with a valuation allowance due to an estimate of the net operating loss carryforward not expected to be realized due to GILTI, due to ownership change limitations from a prior year acquisition as well as certain state net operating loss carryforwards expected to expire unused. Our ability to utilize our U.S. net operating loss carryforwards may be limited in the future if we experience an ownership change as defined by the Internal Revenue Code. At December 31, 2017 , we have various tax credits available to be carried forward including U.S. foreign income tax credits totaling $12.6 million which expire in 2026. The deferred tax assets associated with the U.S. foreign income tax credits expected to expire unused have been fully reserved with a valuation allowance. Income tax credits generated by certain of our foreign subsidiaries in 2017 , 2016 and 2015 have been recognized in our income tax provision. As a result of the deemed repatriation provision of the Tax Act, U.S. income taxes have been provided on approximately $1.1 billion of the undistributed earnings of our foreign subsidiaries at December 31, 2017 . However, we have not provided foreign withholding taxes or state income taxes on the undistributed earnings of our foreign subsidiaries, over which we have sufficient influence to control the distribution of such earnings and have determined that substantially all such earnings have been reinvested indefinitely. These earnings could become subject to foreign withholding tax if they are remitted as dividends. We estimate that repatriation of these foreign earnings would generate withholding taxes and state income taxes of approximately $80.5 million . We operate in and file income tax returns in various U.S. and foreign jurisdictions which are subject to examination by tax authorities. We have tax returns that are open to examination in various jurisdictions for tax years 2010-2017. The open years contain matters that could be subject to differing interpretations of applicable tax laws and regulations related to the amount and/or timing of income, deductions and tax credits. There can be no assurance that the outcome of examinations will be favorable. Our unrecognized tax benefits are subject to change as examinations of specific tax years are completed in the respective jurisdictions. Current examinations include our 2012 and 2013 Philippine income tax returns, 2013-2015 Portuguese income tax returns, and 2010-2014 Malaysian income tax returns. A reconciliation of the beginning and ending gross amount of unrecognized tax benefits is as follows: For the Year Ended December 31 2017 2016 2015 (In thousands) Balance at January 1 $ 23,149 $ 23,332 $ 12,670 Additions based on tax positions related to the current year 1,419 1,822 12,727 Additions for tax positions of prior years 2,661 689 3,341 Reductions for tax positions of prior years (1 ) (2,589 ) (4,815 ) Reductions from lapse of statutes of limitations (17 ) (105 ) (591 ) Balance at December 31 $ 27,211 $ 23,149 $ 23,332 The net increase in our unrecognized tax benefits was $4.1 million from December 31, 2016 to December 31, 2017 . The increases were primarily related to income attribution and income characterization. At December 31, 2017 , all of our gross unrecognized tax benefits would reduce our effective tax rate, if recognized. The liability related to our unrecognized tax benefits is $24.8 million as of December 31, 2017 , and is reported as a component of other non-current liabilities. The unrecognized tax benefits presented in the table above also include positions that have reduced deferred tax assets. The balance of accrued and unpaid interest and penalties is $4.2 million as of December 31, 2017 and is included as a component of other non-current liabilities in connection with our unrecognized tax benefits.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Basic earnings per share (“EPS”) is computed by dividing net income attributable to Amkor common stockholders by the weighted-average number of common shares outstanding during the period. The weighted-average number of common shares outstanding includes restricted shares held by retirement eligible recipients and is reduced for treasury stock. Diluted EPS is computed on the basis of the weighted-average number of shares of common stock plus the effect of dilutive potential common shares outstanding during the period. Dilutive potential common shares include outstanding stock options and unvested restricted shares. The following table summarizes the computations of basic and diluted EPS: For the Year Ended December 31 2017 2016 2015 (In thousands, except per share data) Net income attributable to Amkor $ 260,706 $ 164,190 $ 51,098 Income allocated to participating securities — — (59 ) Net income available to Amkor common stockholders $ 260,706 $ 164,190 $ 51,039 Weighted-average shares outstanding — basic 238,937 237,416 236,850 Effect of dilutive securities: Stock options and restricted share awards 714 618 320 Weighted-average shares outstanding — diluted 239,651 238,034 237,170 Net income attributable to Amkor per common share: Basic $ 1.09 $ 0.69 $ 0.22 Diluted 1.09 0.69 0.22 The following table summarizes the potential shares of common stock that were excluded from diluted EPS, because the effect of including these potential shares was anti-dilutive: For the Year Ended December 31 2017 2016 2015 (In thousands) Stock options and restricted share awards 3,445 1,135 1,858

Factoring of Accounts Receivabl

Factoring of Accounts Receivable	12 Months Ended
	Dec. 31, 2017
Factoring of Accounts Receivable [Abstract]
Factoring of Accounts Receivable	Factoring of Accounts Receivable In certain foreign locations, we use non-recourse factoring arrangements with third party financial institutions to manage our working capital and cash flows. Under this program, we sell receivables to a financial institution for cash at a discount to the face amount. As part of the factoring arrangements, we perform certain collection and administrative functions for the receivables sold. For the year ended December 31, 2017 and 2016 , we sold accounts receivable totaling $611.2 million and $574.1 million , respectively, net of discounts and fees of $4.6 million and $2.5 million , respectively.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories consist of the following: December 31, 2017 2016 (In thousands) Raw materials and purchased components $ 213,649 $ 173,035 Work-in-process 112,843 94,955 Total inventories $ 326,492 $ 267,990

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment consist of the following: December 31, 2017 2016 (In thousands) Land $ 224,894 $ 240,719 Land use rights 26,845 26,845 Buildings and improvements 1,384,846 1,362,007 Machinery and equipment 4,938,291 4,483,523 Software and computer equipment 200,500 205,969 Furniture, fixtures and other equipment 15,722 21,313 Construction in progress 104,910 87,037 Total property, plant and equipment 6,896,008 6,427,413 Less accumulated depreciation and amortization (4,200,943 ) (3,862,765 ) Total property, plant and equipment, net $ 2,695,065 $ 2,564,648 The following table summarizes our depreciation expense: For the Year Ended December 31, 2017 2016 2015 (In thousands) Depreciation expense $ 580,172 $ 552,989 $ 492,458 We had $46.9 million and $44.8 million of costs for our factory and research and development facility in Korea ("K5") in construction in progress as of December 31, 2017 and 2016, respectively. As part of our plan to consolidate factory operations in Korea, we sold the land and buildings comprising our K1 factory in May 2017 for $142.4 million . We received 10% of the sale price at signing in November 2016 and the balance at closing, at which time we recognized a pre-tax gain of $108.1 million .

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill Changes in the carrying amount of goodwill are as follows: Goodwill (In thousands) Balance at December 31, 2015 $ 23,409 Translation adjustment 713 Balance at December 31, 2016 $ 24,122 Translation adjustment 914 Balance at December 31, 2017 $ 25,036 Goodwill relates to the increase in our ownership interest in J-Devices to 100% on December 30, 2015 ( Note 3 ). No goodwill impairment has been identified in any of the years presented.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses consist of the following: December 31, 2017 2016 (In thousands) Payroll and benefits $ 134,785 $ 117,636 Deferred revenue and customer advances 63,196 65,653 Income taxes payable 56,664 37,961 Accrued settlement costs 37,783 35,304 Accrued severance plan obligations (Note 14) 15,190 14,053 Accrued interest 11,873 13,046 Other accrued expenses 55,107 55,016 Total accrued expenses $ 374,598 $ 338,669

Debt

Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt	Debt Short-term borrowings and long-term debt consist of the following: December 31, 2017 2016 (In thousands) Debt of Amkor Technology, Inc.: Senior secured credit facilities: $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019 (1) $ — $ — Senior notes: 6.625% Senior notes, due June 2021 (2) 200,000 400,000 6.375% Senior notes, due October 2022 524,971 524,971 Debt of subsidiaries: Amkor Technology Korea, Inc.: $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due June 2018 (3) 75,000 — Term loan, LIBOR plus 2.70%, due December 2019 55,000 55,000 Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 150,000 150,000 Term loan, fixed rate at 3.70%, due May 2020 (4) 120,000 — Term loan, fund floating rate plus 1.60%, due June 2020 (5) 86,000 86,000 Term loan, LIBOR plus 2.60%, due May 2018 (4) — 120,000 Term loan, foreign currency funding-linked base rate plus 1.33%, due May 2020 (3) — 80,000 J-Devices Corporation: Short-term term loans, variable rates (6) 30,455 22,230 Term loans, fixed rate at 0.53%, due April 2018 6,744 19,460 Term loan, fixed rate at 0.86%, due June 2022 (7) 39,933 — Term loan, fixed rate at 0.60%, due July 2022 (8) 8,430 — Other: Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 (Taiwan) (9) 20,000 20,000 Term loan, LIBOR plus 1.80%, due December 2019 (China) (10) 49,000 — 1,365,533 1,477,661 Less: Unamortized premium and deferred debt costs, net (1,104 ) (2,831 ) Less: Short-term borrowings and current portion of long-term debt (123,848 ) (35,192 ) Long-term debt (including related party) $ 1,240,581 $ 1,439,638 (1) Our $200.0 million senior secured revolving credit facility has a letter of credit sub-limit facility of $25.0 million . Principal is payable at maturity. The availability for the revolving credit facility is based on the amount of our eligible accounts receivable. As of December 31, 2017 , we had availability of $199.4 million under this facility, after reduction of $0.6 million of outstanding standby letters of credit. (2) In July 2017, we redeemed $200.0 million aggregate principal amount of the outstanding $400.0 million of our 6.625% Senior Notes due 2021 ("Notes"), which included $17.5 million held by a related party. In accordance with the terms of the indenture governing the Notes, the redemption price was 101.656% of the principal amount of the Notes, plus accrued and unpaid interest. We recorded a $3.3 million loss on extinguishment related to the premium paid on the call of the Notes and a $1.1 million charge for the write-off of the associated unamortized debt issuance costs. The redemption of the Notes was funded with cash on hand. In 2017 , our related party sold all of its remaining Notes in the open market reducing the long-term debt, related party balance to zero . (3) In April 2017, we decreased the revolving credit facility from $100.0 million to $75.0 million . Principal is payable at maturity, which was extended in June 2017 for one year to June 2018. In April 2017, we borrowed $75.0 million on this facility and repaid the outstanding balance of $80.0 million on our term loan due May 2020. (4) In May 2017, we entered into a $120.0 million term loan agreement to repay the $120.0 million term loan due in 2018. The new term loan agreement extended the maturity date to 2020 and changed the interest rate to a fixed rate. Principal is payable at maturity. (5) In May 2015, we entered into a term loan agreement pursuant to which we may borrow up to $150.0 million for capital expenditures. Principal is payable at maturity. As of December 31, 2017 , $64.0 million was available to be borrowed. (6) We entered into various short-term loans which mature semiannually. Principle is payable in monthly installments. As of December 31, 2017 , $6.2 million was available to be drawn. (7) In June 2017, we entered into a ¥5.0 billion term loan agreement for capital expenditures. Principal is payable in quarterly installments of ¥250.0 million . In June 2017, we borrowed ¥5.0 billion . (8) In July 2017, we entered into a ¥1.0 billion term loan agreement for capital expenditures. Principal is payable in quarterly installments of ¥50.0 million . In July 2017, we borrowed ¥1.0 billion . (9) In November 2015, we entered into a $39.0 million revolving credit facility. Principal is payable at maturity. As of December 31, 2017 , $19.0 million was available to be drawn. (10) In December 2016, we entered into a $50.0 million term loan agreement. Principal is payable in semiannual installments of $0.5 million , with the remaining balance due at maturity. In January 2017, we borrowed $50.0 million . Our foreign debt is generally collateralized by the land, buildings and equipment in the respective locations. The carrying value of the collateral exceeds the carrying amount of the debt. Interest Rates Interest is payable semiannually on our senior notes and quarterly or monthly on our other fixed- and variable-rate debt. Refer to the table above for the interest rates on our fixed-rate debt and to the table below for the interest rates on our variable-rate debt. December 31, 2017 2016 Amkor Technology, Inc.: $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019 — % — % Amkor Technology Korea, Inc.: $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due June 2018 4.01 % — % Term loan, LIBOR plus 2.60%, due May 2018 — % 3.49 % Term loan, LIBOR plus 2.70%, due December 2019 4.02 % 3.54 % Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 4.06 % 3.58 % Term loan, foreign currency funding-linked base rate plus 1.33%, due May 2020 — % 3.59 % Term Loan, fund floating rate plus 1.60%, due June 2020 3.29 % 2.79 % J-Devices Corporation: Short-term credit facilities, variable rates 0.22 % 0.32 % Amkor Technology Taiwan Ltd.: Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 3.18 % 2.78 % Amkor Assembly & Test (Shanghai) Co., Ltd.: Term loan, LIBOR plus 1.80%, due December 2019 3.16 % — % Compliance with Debt Covenants The debt of Amkor Technology, Inc. is structurally subordinated in right of payment to all existing and future debt and other liabilities of our subsidiaries. The agreements governing our indebtedness contain a number of affirmative and negative covenants which restrict our ability to pay dividends and could restrict our operations. We have never paid a dividend to our stockholders and we do not have any present plans for doing so. We were in compliance with all of our covenants at December 31, 2017 and 2016 . Maturities Total Debt (In thousands) Payments due for the year ending December 31, 2018 $ 123,848 2019 173,649 2020 326,649 2021 210,649 2022 530,738 Total debt $ 1,365,533

Pension and Severance Plans

Pension and Severance Plans	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Pension and Severance Plans	Pension and Severance Plans Korean Severance Plan Our subsidiary in Korea maintains an unfunded severance plan that covers certain employees that were employed prior to August 1, 2015. To the extent eligible employees are terminated, our subsidiary in Korea would be required to make lump-sum severance payments on behalf of these eligible employees for service provided prior to August 1, 2015. Factors used to determine severance benefits include employees' length of service, seniority and rate of pay. The employees' length of service and seniority are fixed as of July 31, 2015. The employees' rate of pay is adjusted to the rate of pay at the time of termination. Accrued severance benefits are estimated assuming all eligible employees were to terminate their employment at the balance sheet date. Our contributions to the National Pension Plan of the Republic of Korea are deducted from accrued severance benefit liabilities. On August 1, 2015, our subsidiary in Korea began sponsoring a defined benefit pension plan and a defined contribution plan. Existing employees at that time were given the option of choosing either a defined benefit pension plan or a defined contribution plan for their future benefits and new employees since that date are enrolled in a defined contribution plan. The changes to the balance of our accrued severance plan obligations are as follows: For the Year Ended December 31 2017 2016 2015 (In thousands) Balance at January 1 $ 136,396 $ 143,151 $ 146,880 Provision of severance benefits 11,714 6,746 21,088 Severance payments (11,787 ) (9,429 ) (15,021 ) Foreign currency (gain) loss 17,597 (4,072 ) (9,796 ) Balance at December 31 153,920 136,396 143,151 Payments remaining with the National Pension Fund (185 ) (182 ) (192 ) Total accrued severance plan obligations at December 31 153,735 136,214 142,959 Less current portion of accrued severance plan obligations (Note 12) 15,190 14,053 14,306 Non-current portion of accrued severance plan obligations $ 138,545 $ 122,161 $ 128,653 Foreign Defined Benefit Pension Plans Our subsidiaries in Japan, Korea, Malaysia, the Philippines and Taiwan sponsor defined benefit plans (the “Plans”). Charges to expense are based upon actuarial analyses. The following table summarizes the changes to the Plans’ benefit obligations, fair value of the Plans’ assets and the funded status of the Plans at December 31, 2017 and 2016 : For the Year Ended December 31 2017 2016 (In thousands) Change in projected benefit obligation: Projected benefit obligation at January 1 $ 131,416 $ 109,695 Service cost 33,823 33,854 Interest cost 4,067 3,641 Benefits paid (15,183 ) (8,499 ) Actuarial (gain) loss (1,387 ) (2,801 ) Effects of curtailment 573 — Settlement (2,496 ) (1,165 ) Foreign exchange (gain) loss 7,653 (3,309 ) Projected benefit obligation at December 31 158,466 131,416 Change in plan assets: Fair value of plan assets at January 1 91,471 76,042 Actual gain (loss) on plan assets 8,559 2,876 Employer contributions 28,073 25,114 Settlement (2,496 ) (1,165 ) Benefits paid (15,183 ) (8,499 ) Foreign exchange gain (loss) 5,301 (2,897 ) Fair value of plan assets at December 31 115,725 91,471 Funded status of the Plans at December 31 $ (42,741 ) $ (39,945 ) December 31, 2017 2016 (In thousands) Amounts recognized in the Consolidated Balance Sheets consist of: Prepaid benefit cost (included in non-current assets) $ 656 $ — Accrued benefit liability (included in pension and severance obligations) (43,397 ) (39,945 ) Net amount recognized at year end $ (42,741 ) $ (39,945 ) The accumulated benefit obligation as of December 31, 2017 and 2016 was $113.6 million and $94.5 million , respectively. The following table summarizes, by component, the change in accumulated other comprehensive income (loss), net of tax related to our Plans: Prior Service Cost Actuarial Net Gain (Loss) Total (In thousands) Balance at December 31, 2015 $ 560 $ (1,985 ) $ (1,425 ) Amortization included in net periodic pension cost 22 73 95 Net gain (loss) arising during period — 2,468 2,468 Adjustments to unrealized components of defined benefit pension plan included in other comprehensive income (loss) 22 2,541 2,563 Balance at December 31, 2016 582 556 1,138 Amortization included in net periodic pension cost 21 69 90 Net gain (loss) arising during period — 5,075 5,075 Adjustments to unrealized components of defined benefit pension plan included in other comprehensive income (loss) 21 5,144 5,165 Balance at December 31, 2017 $ 603 $ 5,700 $ 6,303 Estimated amortization of cost to be included in 2018 net periodic pension cost $ 1 $ (147 ) $ (146 ) Information for pension plans with benefit obligations in excess of plan assets is as follows: December 31, 2017 2016 (In thousands) Plans with underfunded or non-funded projected benefit obligation: Aggregate projected benefit obligation $ 119,708 $ 131,416 Aggregate fair value of plan assets 76,313 91,471 Plans with underfunded or non-funded accumulated benefit obligation: Aggregate accumulated benefit obligation 53,720 49,285 Aggregate fair value of plan assets 18,970 16,811 The following table summarizes total pension expense: For the Year Ended December 31 2017 2016 2015 (In thousands) Components of net periodic pension cost and total pension expense: Service cost $ 33,823 $ 33,854 $ 12,481 Interest cost 4,067 3,641 2,954 Expected return on plan assets (4,537 ) (3,788 ) (3,330 ) Amortization of prior service cost 30 35 34 Recognized actuarial (gain) loss 84 94 91 Net periodic pension cost 33,467 33,836 12,230 Curtailment loss 574 — — Settlement (gain) loss 383 128 27 Total pension expense $ 34,424 $ 33,964 $ 12,257 As a result of the adoption of a defined benefit pension plan in Korea beginning on August 1, 2015, and the acquisition of J-Devices on December 30, 2015, our net periodic pension cost has increased from the prior period. The following table summarizes the weighted-average assumptions used in computing the net periodic pension cost and projected benefit obligations: For the Year Ended December 31 2017 2016 2015 Discount rate for determining net periodic pension cost 3.1 % 3.3 % 4.2 % Discount rate for determining benefit obligations at December 31 3.2 % 3.1 % 3.3 % Rate of compensation increase for determining net periodic 3.8 % 3.9 % 4.7 % Rate of compensation increase for determining benefit obligations 3.8 % 3.8 % 3.9 % Expected rate of return on plan assets for determining net periodic 4.9 % 5.0 % 6.2 % The measurement date for determining the Plans’ assets and benefit obligations is December 31, each year. Discount rates are generally derived from yield curves constructed from high-quality corporate or foreign government bonds, for which the timing and amount of cash outflows approximate the estimated payouts. The expected rate of return assumption is based on weighted-average expected returns for each asset class. Expected returns reflect a combination of historical performance analysis and the forward-looking views of the financial markets and include input from our actuaries. We have no control over the direction of our investments in our defined benefit plans in Taiwan as the local Labor Standards Law Fund mandates such contributions into a cash account balance at the Bank of Taiwan. Our defined benefit pension plan in Malaysia is a non-funded plan, and as such, no asset exists related to this plan. Our investment strategies for our defined benefit plans in Japan, Korea and the Philippines, are based on long-term, sustained asset growth through low to medium risk investments. The current rate of return assumption targets are based on asset allocation strategies as follows: Allocation Debt Equity Other Japan defined benefit plan 60 % 37 % 3 % Korea defined benefit plan 40 % 50 % 10 % Philippine defined benefit plan 40 % 56 % 4 % The fair value of our pension plan assets, by asset category utilizing the fair value hierarchy as discussed in Note 16 , is as follows: December 31, 2017 2016 (In thousands) Cash and cash equivalents (Level 1) $ 1,098 $ 10,419 Equity securities U.S. securities (Level 1) 16,854 12,602 Foreign securities (Level 1) 16,826 8,825 Foreign mutual funds (Level 1) 22,193 12,718 55,873 34,145 Debt securities U.S. government bonds (Level 1) 2,188 2,859 U.S. government bonds (Level 2) 830 — U.S. corporate bonds (Level 1) 2,144 1,980 U.S. corporate bonds (Level 2) 5 — Foreign government bonds (Level 1) 5,211 11,001 Foreign government bonds (Level 2) 6,270 7,727 Foreign corporate bonds (Level 1) 520 — Foreign corporate bonds (Level 2) 3,058 1,693 Foreign treasury notes (Level 1) 4,686 — Foreign mutual funds (Level 1) 8,787 10,044 33,699 35,304 Foreign guaranteed investment contracts (Level 2) 14,138 2,445 Taiwan retirement fund (Level 1) 10,094 8,972 Other (Level 1) 584 — Other (Level 2) 239 186 Total fair value of pension plan assets $ 115,725 $ 91,471 The Taiwan retirement fund category of our plan assets represents accounts that our subsidiaries in Taiwan have in a government labor retirement fund in the custody of the Bank of Taiwan. The accounts earn a minimum guaranteed rate of return and are invested in a mix of cash, domestic and foreign equity securities and domestic and foreign debt securities. We expect to make contributions of approximately $23 million during 2018 . We closely monitor the funded status of the Plans with respect to legislative requirements. We intend to make at least the minimum contribution required by law each year. The estimated future benefit payments related to our foreign defined benefit plans are as follows: Payments (In thousands) 2018 $ 6,288 2019 7,516 2020 9,538 2021 11,602 2022 14,143 2023 to 2027 107,557 Defined Contribution Plans We sponsor defined contribution plans in Korea, Malaysia, Taiwan and the U.S. Total defined contribution expense was $10.4 million , $8.8 million and $8.6 million for 2017 , 2016 and 2015 , respectively.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) The following table reflects the changes in accumulated other comprehensive income (loss), net of tax: Defined Benefit Pension Foreign Currency Translation Total (In thousands) Balance at December 31, 2015 $ (1,425 ) $ (659 ) $ (2,084 ) Other comprehensive income (loss) before reclassifications 2,468 5,783 8,251 Amounts reclassified from accumulated other comprehensive income (loss) 95 — 95 Other comprehensive income (loss) 2,563 5,783 8,346 Balance at December 31, 2016 $ 1,138 $ 5,124 $ 6,262 Other comprehensive income (loss) before reclassifications 5,075 11,092 16,167 Amounts reclassified from accumulated other comprehensive income (loss) 90 — 90 Other comprehensive income (loss) 5,165 11,092 16,257 Balance at December 31, 2017 $ 6,303 $ 16,216 $ 22,519 Amounts reclassified out of accumulated other comprehensive income (loss) are included as a component of net periodic pension cost ( Note 14 ) or other (income) expense, net.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The accounting framework for determining fair value includes a hierarchy for ranking the quality and reliability of the information used to measure fair value, which enables the reader of the financial statements to assess the inputs used to develop those measurements. The fair value hierarchy consists of three tiers as follows: Level 1, defined as quoted market prices in active markets for identical assets or liabilities; Level 2, defined as inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, model-based valuation techniques for which all significant assumptions are observable in the market or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3, defined as unobservable inputs that are not corroborated by market data. The fair values of cash, accounts receivable, trade accounts payable, capital expenditures payable, and certain other current assets and accrued expenses approximate carrying values because of their short-term nature. The carrying value of certain other non-current assets and liabilities approximates fair value. Our assets and liabilities recorded at fair value on a recurring basis include cash equivalent money market funds and restricted cash money market funds. We also review goodwill for impairment annually during the fourth quarter of each year. Cash equivalent money market funds and restricted cash money market funds are invested in U.S. money market funds and various U.S. and foreign bank operating and time deposit accounts, which are due on demand or carry a maturity date of less than three months when purchased. No restrictions have been imposed on us regarding withdrawal of balances with respect to our cash equivalents as a result of liquidity or other credit market issues affecting the money market funds we invest in or the counterparty financial institutions holding our deposits. Money market funds are valued using quoted market prices in active markets for identical assets. Recurring fair value measurements consist of the following: December 31, 2017 2016 (In thousands) Cash equivalent money market funds (Level 1) $ 121,627 $ 39,548 Restricted cash money market funds (Level 1) 2,000 2,000 We also measure certain assets and liabilities, including property, plant and equipment and goodwill, at fair value on a nonrecurring basis. We measure the fair value of our debt for disclosure purposes. The following table presents the fair value of financial instruments that are not recorded at fair value on a recurring basis: December 31, 2017 December 31, 2016 Fair Value Carrying Value Fair Value Carrying Value (In thousands) Senior notes (Level 1) $ 745,943 $ 723,867 $ 954,765 $ 922,140 Revolving credit facilities and term loans (Level 2) 639,689 640,562 551,793 552,690 Total financial instruments $ 1,385,632 $ 1,364,429 $ 1,506,558 $ 1,474,830 The estimated fair value of our senior notes is based primarily on quoted market prices reported on or near the respective balance sheet dates. The estimated fair value of our revolving credit facilities and term loans is calculated using a discounted cash flow analysis, which utilizes market based assumptions including forward interest rates adjusted for credit risk.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies We generally warrant that our services will be performed in a professional and workmanlike manner and in compliance with our customers’ specifications. We accrue costs for known warranty issues. Historically, our warranty costs have been immaterial. Legal Proceedings We are involved in claims and legal proceedings and may become involved in other legal matters arising in the ordinary course of our business. We evaluate these claims and legal matters on a case-by-case basis to make a determination as to the impact, if any, on our business, liquidity, results of operations, financial condition or cash flows. Although the outcome of these matters is uncertain, we believe that the ultimate outcome of these claims and proceedings, individually and in the aggregate, will not have a material adverse impact to us. Our evaluation of the potential impact of these claims and legal proceedings on our business, liquidity, results of operations, financial condition or cash flows could change in the future. Settlement of Patent License Litigation Under the terms of a January 2015 patent license litigation settlement, Amkor agreed to pay a total of $155.0 million in 16 equal quarterly recurring payments commencing in the first quarter of 2015, and continuing through the fourth quarter of 2018. During the three months ended December 31, 2014, we recorded a pre-tax charge of $87.1 million , of which $75.3 million was charged to cost of sales and $11.8 million was charged to interest expense. This charge reflected the aggregate amount due under the settlement agreement, net of amounts previously reserved. At December 31, 2017 , the remaining amount we owe under our settlement agreement was $38.8 million . The liability is recorded in accrued expenses ( Note 12 ) in our Consolidated Financial Statements. We will also charge $1.0 million of the amount owed to interest expense over the remaining term of the arrangement. Leases Future minimum lease payments under operating leases that have initial or remaining noncancelable lease terms in excess of one year are: For the Year Ended December 31 (In thousands) 2018 $ 26,439 2019 21,740 2020 13,694 2021 10,530 2022 8,468 Thereafter 28,955 Total future minimum lease payments $ 109,826 Rent expense was $48.1 million , $43.8 million and $24.5 million for 2017 , 2016 and 2015 , respectively. In order to provide packaging and test services, we purchase materials under various long-term supply contracts. Future minimum payments to be made under these contracts for the period 2018 through 2028 are $18.3 million .

Business Segments, Customer Con

Business Segments, Customer Concentrations and Geographic Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Business Segments, Customer Concentrations and Geographic Information	Business Segments, Customer Concentrations and Geographic Information We operate as a single operating segment as managed by our Chief Executive Officer, who is considered our chief operating decision maker ("CODM"). The CODM bears the ultimate responsibility for, and is actively engaged in, the allocation of resources and the evaluation of our operating and financial results. We have concluded that we have a single operating segment based on the following: • We are managed under a functionally-based organizational structure with the head of each function reporting directly to the CODM; • We assess performance, including incentive compensation, based on consolidated operating performance and financial results; • Our CODM allocates resources and makes other operating decisions based on specific customer business opportunities and • We have an integrated process for the design, development and manufacturing services we provide to all of our customers. We also have centralized sales and administrative functions. Net sales by product group consist of the following: For the Year Ended December 31, 2017 2016 2015 (In thousands) Advanced Products $ 1,950,340 $ 1,679,529 $ 1,432,493 Mainstream Products 2,236,157 2,214,106 1,452,110 Total net sales $ 4,186,497 $ 3,893,635 $ 2,884,603 Net sales by region based on customer headquarters location consist of the following: For the Year Ended December 31, 2017 2016 2015 (In thousands) Japan $ 1,208,822 $ 1,158,318 $ 372,810 Asia Pacific (excluding Japan) 827,061 627,177 609,409 Europe, Middle East and Africa 536,552 487,584 489,842 Total foreign countries 2,572,435 2,273,079 1,472,061 United States 1,614,062 1,620,556 1,412,542 Total net sales $ 4,186,497 $ 3,893,635 $ 2,884,603 One customer accounted for 14.3% , 15.8% , and 11.0% of net sales in 2017 , 2016 and 2015 , respectively. A second customer accounted for 12.7% and 14.4% of net sales in 2016 and 2015 , respectively. Net sales for our second customer were below 10% in 2017 . Property, plant and equipment, net, based on physical location, consist of the following: December 31, 2017 2016 (In thousands) China $ 528,739 $ 500,319 Japan 246,223 245,233 Korea 1,131,271 1,130,147 Malaysia 47,922 36,248 Philippines 309,425 313,885 Portugal 64,578 — Taiwan 356,174 326,614 Other foreign countries 216 243 Total foreign countries 2,684,548 2,552,689 United States 10,517 11,959 Total property, plant and equipment, net $ 2,695,065 $ 2,564,648

Quarterly Results (Unaudited)

Quarterly Results (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results (Unaudited)	Quarterly Results (unaudited) The following table sets forth our consolidated unaudited financial data for the last eight quarters ended December 31, 2017 . We believe that we have included all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of our selected quarterly data. The calculation of basic and diluted per share amounts for each quarter is based on the weighted-average shares outstanding for that period; consequently, the sum of the quarters may not necessarily be equal to the full year basic and diluted net income per share. For the Quarter Ended Dec. 31, 2017 (c) Sept. 30, 2017 June 30, 2017 (a) Mar. 31, 2017 Dec. 31, 2016 Sept. 30, 2016 June 30, 2016 Mar. 31, 2016 (In thousands, except per share data) Net sales $ 1,148,423 $ 1,135,027 $ 989,447 $ 913,600 $ 1,021,613 $ 1,086,014 $ 917,326 $ 868,682 Gross profit 225,494 216,638 172,235 142,906 227,187 213,800 131,606 122,884 Operating income (b) 110,128 98,237 168,293 24,655 126,689 114,615 30,542 22,094 Income tax (benefit) expense (12,782 ) 18,752 32,573 439 18,534 24,086 3,360 1,873 Net income (loss) 101,943 55,630 116,459 (9,144 ) 101,202 61,141 5,366 (405 ) Net income (loss) attributable to Amkor 100,770 54,435 115,507 (10,006 ) 100,263 60,089 4,713 (875 ) Net income (loss) attributable to Amkor per common share: Basic $ 0.42 $ 0.23 $ 0.48 $ (0.04 ) $ 0.42 $ 0.25 $ 0.02 $ — Diluted $ 0.42 $ 0.23 $ 0.48 $ (0.04 ) $ 0.42 $ 0.25 $ 0.02 $ — (a) In May 2017, we completed the purchase of Nanium. Nanium's financial results have been included in our Consolidated Financial Statements from the date of acquisition. (b) In May 2017, we sold the land and buildings comprising our K1 factory for $142.4 million which resulted in a pre-tax gain of $108.1 million . (c) In the fourth quarter of 2017, net income includes an estimated net tax benefit of $41.6 million primarily due to the reversal of a valuation allowance on certain U.S. deferred tax assets as a result of the enactment of the Tax Act.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS Balance at Beginning of Period Additions (Credited) Charged to Expense Write-offs (a) Other Balance at End of Period (In thousands) Deferred tax asset valuation allowance: Year ended December 31, 2015 $ 149,847 18,507 (248 ) (1 ) $ 168,105 Year ended December 31, 2016 $ 168,105 7,729 (15,091 ) 4,624 $ 165,367 Year ended December 31, 2017 $ 165,367 (116,917 ) (489 ) 35,377 $ 83,338 (a) Column represents adjustments to the deferred tax asset valuation allowance established as part of the purchase accounting related to Amkor's acquisition of Nanium in 2017 and adjustments directly through stockholders’ equity for changes in accumulated other comprehensive income (loss) related to our foreign defined benefit pension plans and the adoption of ASU 2016-09 on July 1, 2016.

Description of Business and S28

Description of Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Amkor is one of the world’s leading providers of outsourced semiconductor packaging and test services. Amkor pioneered the outsourcing of semiconductor packaging and test services through a predecessor corporation in 1968, and over the years we have built a leading position by: • Designing and developing innovative packaging and test technologies; • Offering a broad portfolio of cost-effective solutions and services; • Focusing on strategic end markets that offer solid growth potential; • Cultivating long-standing relationships with our customers, which include many of the world’s leading semiconductor companies; • Collaborating with customers, original equipment manufacturers ("OEMs") and equipment and material suppliers; • Developing a competitive cost structure with disciplined capital investment; • Building expertise in high-volume manufacturing processes and developing a reputation for high quality and solid execution and • Providing a geographically diverse operating base, with research and development, engineering support and production capabilities at various facilities throughout China, Japan, Korea, Malaysia, the Philippines, Portugal and Taiwan.
Basis of Presentation	Basis of Presentation Our Consolidated Financial Statements include the accounts of Amkor Technology, Inc. and our subsidiaries (“Amkor”). Our Consolidated Financial Statements reflect the elimination of all significant inter-company accounts and transactions. On December 30, 2015 , we increased our investment in J-Devices to 100% ( Note 3 ). As a result, our accounting for J-Devices changed from the equity method to the consolidation method effective December 30, 2015. The operating results of J-Devices were consolidated beginning in 2016. On May 22, 2017, we completed the purchase of Nanium, S.A. ("Nanium"). Nanium's financial results have been included in our Consolidated Financial Statements from the date of acquisition ( Note 3 ). Our investments in variable interest entities in which we are the primary beneficiary are consolidated. We reflect the remaining portion of variable interest entities and foreign subsidiaries that are not wholly owned as noncontrolling interests.
Use of Estimates	The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, we evaluate our estimates, including those related to acquisitions, revenue recognition, income taxes, inventory, long lived assets and contingencies. These estimates are based on management’s best knowledge of current events, historical experience, actions that we may undertake in the future and on various other assumptions that are believed to be reasonable under the circumstances. As a result, actual results could differ materially from these estimates and assumptions.
Consolidation of Variable Interest Entities	Consolidation of Variable Interest Entities We have variable interests in certain Philippine realty corporations in which we have a 40% ownership. We lease land and buildings in the Philippines from these entities and we are the primary beneficiary of these arrangements. As of December 31, 2017 , the combined book value of the assets and liabilities associated with these Philippine realty corporations included in our Consolidated Balance Sheet was $16.9 million and $0.4 million , respectively. The impact of consolidating these variable interest entities on our Consolidated Statements of Income was not significant, and other than our lease payments, we have not provided any significant assistance or other financial support to these variable interest entities for the years ended December 31, 2017 , 2016 or 2015 . The creditors of the Philippine realty corporations have no recourse to our general credit.
Foreign Currency Translation	Foreign Currency Translation The U.S. dollar is the functional currency of our subsidiaries other than J-Devices, and the foreign currency asset and liability amounts at these subsidiaries are remeasured into U.S. dollars at end-of-period exchange rates, except for nonmonetary items which are remeasured at historical rates. Foreign currency income and expenses are remeasured at daily exchange rates, except for expenses related to balance sheet amounts which are remeasured at historical exchange rates. Exchange gains and losses arising from remeasurement of foreign currency-denominated monetary assets and liabilities are included in other (income) expense, net in the period in which they occur. The Japanese Yen is the functional currency of J-Devices. The asset and liability amounts of J-Devices are translated into U.S. dollars at end-of-period exchange rates. Income and expenses are translated into U.S. dollars at average exchange rates in effect during the period. The resulting translation adjustments are reported as a component of accumulated other comprehensive income in the stockholders’ equity section of the balance sheet. Assets and liabilities denominated in a currency other than the functional currency are remeasured into the functional currency prior to translation into U.S. dollars, and the resulting transaction exchange gains or losses are included in other expense (income) in the period in which they occur.
Risks and Concentrations	Risks and Concentrations The semiconductor industry is characterized by rapid technological change, competitive pricing pressures and cyclical market patterns. Our financial results are affected by a wide variety of factors, including general economic conditions worldwide, economic conditions specific to the semiconductor industry, the timely implementation of new package and test technologies, the ability to safeguard patents and intellectual property in a rapidly evolving market and reliance on materials and equipment suppliers. In addition, the semiconductor market has historically been cyclical and subject to significant economic downturns at various times. Our profitability and ability to generate cash from operations is principally dependent upon demand for semiconductors, the utilization of our capacity, semiconductor package mix, the average selling price of our services, our ability to manage our capital expenditures and our ability to control our costs including labor, material, overhead and financing costs. A significant portion of our revenues is concentrated with a small group of customers ( Note 18 ). The loss of a significant customer, a business combination among customers, a reduction in orders or decrease in price from a significant customer or disruption in any of our significant strategic partnerships or other commercial arrangements could have a material adverse effect on our business, liquidity, results of operations, financial condition and cash flows. Financial instruments, for which we are subject to credit risk, consist principally of accounts receivable and cash and cash equivalents. With respect to accounts receivable, we mitigate our credit risk by selling primarily to well-established companies, performing ongoing credit evaluations and making frequent contact with customers. In addition, we may utilize non-recourse factoring to mitigate credit risk when considered appropriate. We have historically mitigated our credit risk with respect to cash and cash equivalents through diversification of our holdings into various high quality money market funds and bank deposit accounts. At December 31, 2017 , our cash and cash equivalents were maintained in various U.S. and foreign bank operating and time deposit accounts and invested in U.S. money market funds.
Contingencies and Litigation	Contingencies and Litigation We may be subject to certain legal proceedings, lawsuits and other claims, as discussed in Note 17 . We accrue for a loss contingency, including legal proceedings, lawsuits, pending claims and other legal matters, when we conclude that the likelihood of a loss is probable and the amount of the loss can be reasonably estimated. When the reasonable estimate of the loss is within a range of amounts, and no amount in the range constitutes a better estimate than any other amount, we accrue for the amount at the low end of the range. We adjust our accruals from time to time as we receive additional information, but the loss we incur may be significantly greater than or less than the amount we have accrued. We disclose loss contingencies if we believe they are material and there is at least a reasonable possibility that a loss has been incurred. Attorney fees related to legal matters are expensed as incurred.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Our cash and cash equivalents are maintained in various U.S. and foreign bank operating and time deposit accounts and invested in U.S. money market funds.
Restricted Cash	Restricted Cash Restricted cash, current, consists of short-term cash equivalents used to collateralize our daily banking services. Restricted cash, non-current, mainly consists of collateral to fulfill foreign trade compliance requirements.
Inventories	Inventories Inventories are stated at the lower of cost and net realizable value. Cost is principally determined by standard cost or the weighted moving average method, both of which approximate actual cost. We review and set our standard costs as needed, but at a minimum on an annual basis. We reduce the carrying value of our inventories for the cost of inventory we estimate is excess and obsolete based on the age of our inventories. When a determination is made that the inventory will not be utilized in production or is not saleable, it is written-off.
Other Current Assets	Other Current Assets Other current assets consist principally of prepaid assets and an investment in government securities by a foreign subsidiary to satisfy local regulatory requirements, which is recorded at amortized cost.
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment are stated at cost. Depreciation is calculated by the straight-line method over the estimated useful lives of depreciable assets which are as follows: Land use rights 50 to 90 years Buildings and improvements 10 to 40 years Machinery and equipment 2 to 7 years Software and computer equipment 3 to 5 years Furniture, fixtures and other equipment 4 to 10 years Cost and accumulated depreciation for property retired or disposed of are removed from the accounts, and any resulting gain or loss is included in earnings. Expenditures for maintenance and repairs are charged to expense as incurred. We review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. Recoverability of a long-lived asset group to be held and used in operations is measured by a comparison of the carrying amount to the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the asset group. If such asset group is considered to be impaired, the impairment loss is measured as the amount by which the carrying amount of the asset group exceeds its fair value. Long-lived assets to be disposed of are carried at the lower of cost or fair value less the costs of disposal.
Goodwill	Goodwill Goodwill is recorded when the cost of an acquisition exceeds the fair value of the net tangible and identifiable intangible assets acquired. We review goodwill for impairment annually during the fourth quarter of each year and whenever events or changes in circumstances indicate that an impairment may exist. Impairment losses are recorded when the carrying amount of the reporting unit exceeds its fair value.
Other Assets	Other Assets Other assets consist principally of deferred tax assets and refundable security deposits.
Fair Value Measurements	Fair Value Measurements We apply fair value accounting for assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring or nonrecurring basis. We define fair value as the price that would be received from selling an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. See Note 16 for further discussion of fair value measurements.
Revenue Recognition	Revenue Recognition We recognize revenue from our packaging and test services, net of value-added or other similar taxes, when there is evidence of an arrangement, delivery has occurred or services have been rendered, fees are fixed or determinable and collectibility is reasonably assured. Generally, these criteria are met and revenue is recognized upon shipment or, in some cases, customer acceptance. If the revenue recognition criteria are not met, we defer the revenue. Deferred revenue generally results from two types of transactions: contractual invoicing at interim points in the packaging and test process prior to shipment of the finished product and customer advances for supply agreements with customers where we commit capacity in exchange for customer prepayment of services. These prepayments are deferred and recorded as customer advances within accrued expenses and other non-current liabilities. We generally do not take ownership of customer-supplied semiconductor wafers. Title and risk of loss remains with the customer for these materials at all times. Accordingly, the cost of the customer-supplied materials is not included in our Consolidated Financial Statements. An allowance for sales credits is recorded as a reduction to sales and accounts receivable during the period of sale such that accounts receivable is reported at its estimated net realizable value. The allowance for sales credits is an estimate of the future credits we will issue for billing adjustments primarily for invoicing corrections and miscellaneous customer claims and is estimated based upon recent credit issuance, historical experience and specific identification of known or expected sales credits at the end of the reporting period. Additionally, provisions are made for doubtful accounts when there is doubt as to the collectibility of accounts receivable. The allowance for doubtful accounts is recorded as bad debt expense and is classified as selling, general and administrative expense. The allowance for doubtful accounts is based upon specific identification of doubtful accounts considering the age of the receivable balance, the customer’s historical payment history and current credit worthiness as well as specific identification of any known or expected collectibility issues. Historically, our allowance for doubtful accounts has been immaterial.
Shipping and Handling Fees and Costs	Shipping and Handling Fees and Costs Amounts billed to customers for shipping and handling are presented in net sales. Costs incurred for shipping and handling are included in cost of sales.
Research and Development Costs	Research and Development Costs Research and development expenses include costs attributable to the conduct of research and development programs primarily related to the development of new package designs or technologies and improving the efficiency and capabilities of our existing production processes. Such costs include salaries, payroll taxes, employee benefit costs, materials, supplies, depreciation and maintenance of research equipment, services provided by outside contractors and the allocable portions of facility costs such as rent, utilities, insurance, repairs and maintenance, depreciation and general support services. All costs associated with research and development are expensed as incurred.
Income Taxes	Income Taxes Income taxes are accounted for using the asset and liability method. Under this method, deferred income tax assets and liabilities are recognized for the future tax consequences attributable to temporary differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis as well as for net operating loss and tax credit carryforwards. Deferred income tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which these temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is provided for those deferred tax assets for which it is more likely than not that the related tax benefits will not be realized. We monitor on an ongoing basis our ability to utilize our deferred tax assets and whether there is a need for a related valuation allowance. In evaluating our ability to recover our deferred tax assets in the jurisdictions from which they arise, we consider all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax-planning strategies and results of recent operations. For most of our U.S. and foreign deferred tax assets, we consider it more likely than not that we will have sufficient taxable income to allow us to realize these deferred tax assets. However, in the event taxable income falls short of current expectations, we may need to establish a valuation allowance against such deferred tax assets. ASC 740, Accounting for Income Taxes, requires companies to recognize the effect of tax law changes in the period of enactment even though the effective date for most provisions is for tax years beginning after December 31, 2017. Given the significance of the Tax Act, the SEC staff issued Staff Accounting Bulletin No. 118, which allows registrants to record provisional amounts during a one year “measurement period” similar to that used when accounting for business combinations. However, the measurement period is deemed to have ended earlier when the registrant has obtained, prepared and analyzed the information necessary to finalize its accounting. During the measurement period, impacts of the law are expected to be recorded at the time a reasonable estimate for all or a portion of the effects can be made, and provisional amounts can be recognized and adjusted as information becomes available, prepared or analyzed. We have reported provisional amounts for the income tax effects of the Tax Act for which the accounting is incomplete but a reasonable estimate could be determined. There were no specific impacts of the Tax Act that could not be reasonably estimated. Our estimate of the impact of the Tax Act may be adjusted throughout the allowable measurement period as we collect additional information, prepare and analyze the information and evaluate any regulatory guidance or clarifications. Our review is expected to include: • One-time transition tax: Further information is required to substantiate the underlying data supporting foreign earnings and profits, foreign tax credits, and amounts held in liquid and illiquid assets at various measurement dates. Changes to our provisional estimates and further analysis could impact our judgments, elections and assertions. • Remeasurement of deferred tax assets and liabilities: Further analysis is required to calculate the impact on the related account balances including the impact of complex new provisions which include the Base Erosion Anti-abuse Tax and Global Intangible Low-Taxed Income (“GILTI”), designed to subject certain foreign earnings to U.S. tax. • Valuation allowances: We have assessed whether valuation allowance analyses for deferred tax assets are affected by various aspects of the Tax Act (for example one-time transition tax, GILTI, new categories of foreign tax credits). Since we have recorded provisional amounts related to the provisions of the Tax Act, any corresponding determination of the need for a change in a valuation allowance is also provisional. We recognize in our Consolidated Financial Statements the impact of an income tax position, if that position is more likely than not of being sustained on audit, based on the technical merits of the position. Related interest and penalties are classified as income taxes in the financial statements. See Note 6 for more information regarding unrecognized income tax benefits. We monitor on an ongoing basis our ability to utilize our deferred tax assets and whether there is a need for a related valuation allowance. In evaluating our ability to recover our deferred tax assets in the jurisdictions from which they arise, we consider all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, tax-planning strategies and results of recent operations. For most of our U.S. and foreign deferred tax assets, we consider it more likely than not that we will have sufficient taxable income to allow us to realize these deferred tax assets.

Description of Business and S29

Description of Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Property Plant and Equipment Policy	Depreciation is calculated by the straight-line method over the estimated useful lives of depreciable assets which are as follows: Land use rights 50 to 90 years Buildings and improvements 10 to 40 years Machinery and equipment 2 to 7 years Software and computer equipment 3 to 5 years Furniture, fixtures and other equipment 4 to 10 years

New Accounting Standards (Table

New Accounting Standards (Tables)	12 Months Ended
	Dec. 31, 2017
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	We are in the process of finalizing the impact that this new standard will have on our consolidated financial statements and disclosure; however, we expect the following impacts to our reported results: For the Year Ended December 31, 2017 As Reported New Revenue Standard Adjustment (Estimate) As Adjusted (Estimate) (In thousands, except per share data) Income Statement: Net sales $ 4,186,497 $ 24,000 $ 4,210,497 Cost of sales 3,429,224 17,000 3,446,224 Net income 264,888 5,000 269,888 Net income attributable to Amkor per common share: Basic 1.09 0.02 1.11 Diluted 1.09 0.02 1.11 For the Year Ended December 31, 2016 As Reported New Revenue As Adjusted (In thousands, except per share data) Income Statement: Net sales $ 3,893,635 $ 36,000 $ 3,929,635 Cost of sales 3,198,158 21,000 3,219,158 Net income 167,304 11,000 178,304 Net income attributable to Amkor per common share: Basic 0.69 0.05 0.74 Diluted 0.69 0.04 0.73 December 31, 2017 As New Revenue As Adjusted (In thousands) Balance Sheet: Accounts receivable, net $ 692,287 $ 106,000 $ 798,287 Inventories 326,492 (113,000 ) 213,492 Accrued expenses 374,598 (48,000 ) 326,598 Accumulated deficit (42,851 ) 31,000 (11,851 )

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Summary of Consideration Transferred and Identifiable Assets and Liabilities Assumed	The following table summarizes the consideration transferred to acquire J-Devices and the amounts of identifiable assets acquired and liabilities assumed at the acquisition date: (In thousands) Fair value of consideration transferred: Cash $ 105,391 Fair value of our previously held equity interest in J-Devices 160,087 Total $ 265,478 Recognized amounts of identifiable assets acquired and liabilities assumed: Cash $ 127,968 Accounts receivable 180,177 Inventory 42,502 Other current assets 2,363 Property, plant and equipment 230,319 Other assets 9,268 Short-term borrowings and current portion of long-term debt (36,770 ) Other current liabilities (251,405 ) Long-term debt (18,885 ) Pension obligations (22,250 ) Other non-current liabilities (21,218 ) Total identifiable net assets 242,069 Goodwill 23,409 Total $ 265,478
Schedule of Pro Forma Information	The pro forma information does not include any potential revenue enhancements, cost synergies or other operating efficiencies that could result from the acquisition. For the Year Ended December 31 2015 2014 (unaudited) (unaudited) (In thousands, except per share data) Net sales $ 3,696,495 $ 4,051,076 Net income 88,190 153,049 Net income attributable to Amkor 85,394 149,548 Basic earnings per share 0.36 0.65 Diluted earnings per share 0.36 0.63

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of all common stock option activity	The following table summarizes our stock option activity for the year ended December 31, 2017 : Number of Shares (In thousands) Weighted-Average Exercise Price per Share Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (In thousands) Outstanding at December 31, 2016 2,443 $ 6.93 Granted 2,900 9.97 Exercised (469) 6.66 Forfeited or expired (122) 5.12 Outstanding at December 31, 2017 4,752 $ 8.86 7.51 $ 6,403 Fully vested at December 31, 2017 and expected to vest thereafter 4,632 $ 8.83 7.46 $ 6,369 Exercisable at December 31, 2017 1,733 $ 7.17 4.75 $ 5,455
Assumptions used in valuing the weighted average fair values of the options granted	The following assumptions were used to calculate the weighted-average fair values of the options granted: For the Year Ended December 31, 2017 2016 2015 Expected life (in years) 5.7 6.5 5.8 Risk-free interest rate 1.9 % 1.5 % 1.8 % Volatility 43 % 48 % 45 % Dividend yield — — — Weighted-average grant date fair value per option granted $ 4.24 $ 2.89 $ 3.14
Restricted share activity	The following table summarizes our restricted share activity for the year ended December 31, 2017 : Number of Shares (In thousands) Weighted- average Grant Date Fair Value (Per Share) Nonvested at December 31, 2016 145 $ 5.02 Awards granted 224 10.06 Awards vested (181 ) 5.93 Awards forfeited — — Nonvested at December 31, 2017 188 10.15

Other Income and Expense (Table

Other Income and Expense (Tables)	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Schedule of Other Nonoperating Income (Expense)	Other income and expense consists of the following: For the Year Ended December 31, 2017 2016 2015 (In thousands) Interest income $ (3,215 ) $ (1,326 ) $ (2,539 ) Foreign currency (gain) loss, net 11,823 (3,592 ) (7,849 ) Loss on debt retirement 4,835 — 9,560 Loss from acquisition of J-Devices (Note 3) — — 13,501 Other (income) expense, net (1,554 ) (936 ) (2,122 ) Total other (income) expense, net $ 11,889 $ (5,854 ) $ 10,551

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	Geographic sources of income (loss) before taxes and equity in earnings of unconsolidated affiliate are as follows: For the Year Ended December 31, 2017 2016 2015 (In thousands) United States $ 14,935 $ (12,385 ) $ (39,684 ) Foreign 288,935 227,542 107,596 Income before taxes and equity in earnings of unconsolidated affiliate $ 303,870 $ 215,157 $ 67,912
Schedule of Components of Income Tax Expense (Benefit)	The components of the provision (benefit) for income taxes are as follows: For the Year Ended December 31 2017 2016 2015 (In thousands) Current: Federal $ — $ — $ — State 11 22 11 Foreign 81,969 49,577 28,721 81,980 49,599 28,732 Deferred: Federal (36,943 ) — — State (4,611 ) — — Foreign (1,444 ) (1,746 ) (697 ) (42,998 ) (1,746 ) (697 ) Income tax expense $ 38,982 $ 47,853 $ 28,035
Schedule of Effective Income Tax Rate Reconciliation	The reconciliation between the U.S. federal statutory income tax rate of 35% and our income tax expense is as follows: For the Year Ended December 31 2017 2016 2015 (In thousands) U.S. federal tax at 35% $ 106,354 $ 75,305 $ 23,769 State taxes, net of federal benefit 2,193 836 2,622 Foreign income taxed at different rates (51,412 ) (17,907 ) (11,756 ) Foreign exchange (loss) gain 29,756 (1,127 ) (5,680 ) Change in valuation allowance (4,703 ) (7,362 ) 18,259 Adjustments related to prior years 3,329 (2,648 ) (912 ) U.S. tax reform (the Tax Act) (41,554 ) — — Income tax credits generated (7,296 ) (40,301 ) (1,919 ) Repatriation of foreign earnings and profits 719 25,604 91 Expiration of net operating losses and credits 166 15,092 74 Non-deductible loss on acquisition of J-Devices (Note 3) — — 4,725 Other 1,430 361 (1,238 ) Income tax expense $ 38,982 $ 47,853 $ 28,035
Schedule of Income Tax Expense (Benefit) Impact of Tax Cuts and Jobs Act of 2017	In 2017, we recognized a net benefit for the impact of the Tax Act with components as follows: (In thousands) One-time transition tax before credits $ 162,750 Tax credits (128,395 ) Remeasure deferred tax assets 36,794 Release valuation allowance (112,703 ) Net impact of the Tax Act $ (41,554 )
Schedule of Deferred Tax Assets and Liabilities	The following is a summary of the components of our deferred tax assets and liabilities: December 31, 2017 2016 (In thousands) Deferred tax assets: Net operating loss carryforwards $ 53,130 $ 111,899 Income tax credits 23,998 41,900 Property, plant and equipment 35,479 21,860 Accrued liabilities 68,091 68,563 Receivable 32,719 — Unrealized foreign exchange loss 1,924 531 Other 12,682 14,583 Total deferred tax assets 228,023 259,336 Valuation allowance (83,338 ) (165,367 ) Total deferred tax assets net of valuation allowance 144,685 93,969 Deferred tax liabilities: Property, plant and equipment 15,754 20,407 Deferred gain 939 2,655 Unrealized foreign exchange gain 8,383 990 Other 4,566 4,836 Total deferred tax liabilities 29,642 28,888 Net deferred tax assets $ 115,043 $ 65,081 Recognized as: Other assets 117,608 66,831 Other non-current liabilities (2,565 ) (1,750 ) Total $ 115,043 $ 65,081
Summary of Operating Loss Carryforwards	Our net operating loss carryforwards (“NOL’s”) are as follows: December 31, 2017 2016 Expiration (In thousands) U.S. Federal NOL’s $ 220,445 $ 292,715 2021-2037 U.S. State NOL’s 121,095 138,218 2018-2036 Foreign NOL’s 2,967 3,378 2018-2025
Schedule of Unrecognized Tax Benefits Rollforward	A reconciliation of the beginning and ending gross amount of unrecognized tax benefits is as follows: For the Year Ended December 31 2017 2016 2015 (In thousands) Balance at January 1 $ 23,149 $ 23,332 $ 12,670 Additions based on tax positions related to the current year 1,419 1,822 12,727 Additions for tax positions of prior years 2,661 689 3,341 Reductions for tax positions of prior years (1 ) (2,589 ) (4,815 ) Reductions from lapse of statutes of limitations (17 ) (105 ) (591 ) Balance at December 31 $ 27,211 $ 23,149 $ 23,332
Summary of Valuation Allowance	Valuation allowance against deferred tax assets consist of the following: December 31, 2017 2016 (In thousands) Valuation allowance: U.S. $ 43,719 $ 164,479 Portugal 39,009 — Other 610 888 Total valuation allowance $ 83,338 $ 165,367

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Computation of basic and diluted earnings per share	The following table summarizes the computations of basic and diluted EPS: For the Year Ended December 31 2017 2016 2015 (In thousands, except per share data) Net income attributable to Amkor $ 260,706 $ 164,190 $ 51,098 Income allocated to participating securities — — (59 ) Net income available to Amkor common stockholders $ 260,706 $ 164,190 $ 51,039 Weighted-average shares outstanding — basic 238,937 237,416 236,850 Effect of dilutive securities: Stock options and restricted share awards 714 618 320 Weighted-average shares outstanding — diluted 239,651 238,034 237,170 Net income attributable to Amkor per common share: Basic $ 1.09 $ 0.69 $ 0.22 Diluted 1.09 0.69 0.22
Antidilutive effect of potential shares of common stock that were excluded from diluted earnings per share	The following table summarizes the potential shares of common stock that were excluded from diluted EPS, because the effect of including these potential shares was anti-dilutive: For the Year Ended December 31 2017 2016 2015 (In thousands) Stock options and restricted share awards 3,445 1,135 1,858

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventories	Inventories consist of the following: December 31, 2017 2016 (In thousands) Raw materials and purchased components $ 213,649 $ 173,035 Work-in-process 112,843 94,955 Total inventories $ 326,492 $ 267,990

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of Property, plant and equipment	Property, plant and equipment consist of the following: December 31, 2017 2016 (In thousands) Land $ 224,894 $ 240,719 Land use rights 26,845 26,845 Buildings and improvements 1,384,846 1,362,007 Machinery and equipment 4,938,291 4,483,523 Software and computer equipment 200,500 205,969 Furniture, fixtures and other equipment 15,722 21,313 Construction in progress 104,910 87,037 Total property, plant and equipment 6,896,008 6,427,413 Less accumulated depreciation and amortization (4,200,943 ) (3,862,765 ) Total property, plant and equipment, net $ 2,695,065 $ 2,564,648 The following table summarizes our depreciation expense: For the Year Ended December 31, 2017 2016 2015 (In thousands) Depreciation expense $ 580,172 $ 552,989 $ 492,458

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Changes in the carrying amount of goodwill are as follows: Goodwill (In thousands) Balance at December 31, 2015 $ 23,409 Translation adjustment 713 Balance at December 31, 2016 $ 24,122 Translation adjustment 914 Balance at December 31, 2017 $ 25,036

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Summarized Accrued expenses	Accrued expenses consist of the following: December 31, 2017 2016 (In thousands) Payroll and benefits $ 134,785 $ 117,636 Deferred revenue and customer advances 63,196 65,653 Income taxes payable 56,664 37,961 Accrued settlement costs 37,783 35,304 Accrued severance plan obligations (Note 14) 15,190 14,053 Accrued interest 11,873 13,046 Other accrued expenses 55,107 55,016 Total accrued expenses $ 374,598 $ 338,669

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Summary of Short term Borrowings And Long term Debt	Short-term borrowings and long-term debt consist of the following: December 31, 2017 2016 (In thousands) Debt of Amkor Technology, Inc.: Senior secured credit facilities: $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019 (1) $ — $ — Senior notes: 6.625% Senior notes, due June 2021 (2) 200,000 400,000 6.375% Senior notes, due October 2022 524,971 524,971 Debt of subsidiaries: Amkor Technology Korea, Inc.: $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due June 2018 (3) 75,000 — Term loan, LIBOR plus 2.70%, due December 2019 55,000 55,000 Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 150,000 150,000 Term loan, fixed rate at 3.70%, due May 2020 (4) 120,000 — Term loan, fund floating rate plus 1.60%, due June 2020 (5) 86,000 86,000 Term loan, LIBOR plus 2.60%, due May 2018 (4) — 120,000 Term loan, foreign currency funding-linked base rate plus 1.33%, due May 2020 (3) — 80,000 J-Devices Corporation: Short-term term loans, variable rates (6) 30,455 22,230 Term loans, fixed rate at 0.53%, due April 2018 6,744 19,460 Term loan, fixed rate at 0.86%, due June 2022 (7) 39,933 — Term loan, fixed rate at 0.60%, due July 2022 (8) 8,430 — Other: Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 (Taiwan) (9) 20,000 20,000 Term loan, LIBOR plus 1.80%, due December 2019 (China) (10) 49,000 — 1,365,533 1,477,661 Less: Unamortized premium and deferred debt costs, net (1,104 ) (2,831 ) Less: Short-term borrowings and current portion of long-term debt (123,848 ) (35,192 ) Long-term debt (including related party) $ 1,240,581 $ 1,439,638 (1) Our $200.0 million senior secured revolving credit facility has a letter of credit sub-limit facility of $25.0 million . Principal is payable at maturity. The availability for the revolving credit facility is based on the amount of our eligible accounts receivable. As of December 31, 2017 , we had availability of $199.4 million under this facility, after reduction of $0.6 million of outstanding standby letters of credit. (2) In July 2017, we redeemed $200.0 million aggregate principal amount of the outstanding $400.0 million of our 6.625% Senior Notes due 2021 ("Notes"), which included $17.5 million held by a related party. In accordance with the terms of the indenture governing the Notes, the redemption price was 101.656% of the principal amount of the Notes, plus accrued and unpaid interest. We recorded a $3.3 million loss on extinguishment related to the premium paid on the call of the Notes and a $1.1 million charge for the write-off of the associated unamortized debt issuance costs. The redemption of the Notes was funded with cash on hand. In 2017 , our related party sold all of its remaining Notes in the open market reducing the long-term debt, related party balance to zero . (3) In April 2017, we decreased the revolving credit facility from $100.0 million to $75.0 million . Principal is payable at maturity, which was extended in June 2017 for one year to June 2018. In April 2017, we borrowed $75.0 million on this facility and repaid the outstanding balance of $80.0 million on our term loan due May 2020. (4) In May 2017, we entered into a $120.0 million term loan agreement to repay the $120.0 million term loan due in 2018. The new term loan agreement extended the maturity date to 2020 and changed the interest rate to a fixed rate. Principal is payable at maturity. (5) In May 2015, we entered into a term loan agreement pursuant to which we may borrow up to $150.0 million for capital expenditures. Principal is payable at maturity. As of December 31, 2017 , $64.0 million was available to be borrowed. (6) We entered into various short-term loans which mature semiannually. Principle is payable in monthly installments. As of December 31, 2017 , $6.2 million was available to be drawn. (7) In June 2017, we entered into a ¥5.0 billion term loan agreement for capital expenditures. Principal is payable in quarterly installments of ¥250.0 million . In June 2017, we borrowed ¥5.0 billion . (8) In July 2017, we entered into a ¥1.0 billion term loan agreement for capital expenditures. Principal is payable in quarterly installments of ¥50.0 million . In July 2017, we borrowed ¥1.0 billion . (9) In November 2015, we entered into a $39.0 million revolving credit facility. Principal is payable at maturity. As of December 31, 2017 , $19.0 million was available to be drawn. (10) In December 2016, we entered into a $50.0 million term loan agreement. Principal is payable in semiannual installments of $0.5 million , with the remaining balance due at maturity. In January 2017, we borrowed $50.0 million .
Schedule of Interest Rates	Refer to the table above for the interest rates on our fixed-rate debt and to the table below for the interest rates on our variable-rate debt. December 31, 2017 2016 Amkor Technology, Inc.: $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019 — % — % Amkor Technology Korea, Inc.: $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due June 2018 4.01 % — % Term loan, LIBOR plus 2.60%, due May 2018 — % 3.49 % Term loan, LIBOR plus 2.70%, due December 2019 4.02 % 3.54 % Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 4.06 % 3.58 % Term loan, foreign currency funding-linked base rate plus 1.33%, due May 2020 — % 3.59 % Term Loan, fund floating rate plus 1.60%, due June 2020 3.29 % 2.79 % J-Devices Corporation: Short-term credit facilities, variable rates 0.22 % 0.32 % Amkor Technology Taiwan Ltd.: Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 3.18 % 2.78 % Amkor Assembly & Test (Shanghai) Co., Ltd.: Term loan, LIBOR plus 1.80%, due December 2019 3.16 % — %
Schedule of Maturities of Long-term Debt	Maturities Total Debt (In thousands) Payments due for the year ending December 31, 2018 $ 123,848 2019 173,649 2020 326,649 2021 210,649 2022 530,738 Total debt $ 1,365,533

Pension and Severance Plans (Ta

Pension and Severance Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Schedule Of Accrued Severance Obligation	The changes to the balance of our accrued severance plan obligations are as follows: For the Year Ended December 31 2017 2016 2015 (In thousands) Balance at January 1 $ 136,396 $ 143,151 $ 146,880 Provision of severance benefits 11,714 6,746 21,088 Severance payments (11,787 ) (9,429 ) (15,021 ) Foreign currency (gain) loss 17,597 (4,072 ) (9,796 ) Balance at December 31 153,920 136,396 143,151 Payments remaining with the National Pension Fund (185 ) (182 ) (192 ) Total accrued severance plan obligations at December 31 153,735 136,214 142,959 Less current portion of accrued severance plan obligations (Note 12) 15,190 14,053 14,306 Non-current portion of accrued severance plan obligations $ 138,545 $ 122,161 $ 128,653
Schedule of Changes in Projected Benefit Obligations and Fair Value of Plan Assets	The following table summarizes the changes to the Plans’ benefit obligations, fair value of the Plans’ assets and the funded status of the Plans at December 31, 2017 and 2016 : For the Year Ended December 31 2017 2016 (In thousands) Change in projected benefit obligation: Projected benefit obligation at January 1 $ 131,416 $ 109,695 Service cost 33,823 33,854 Interest cost 4,067 3,641 Benefits paid (15,183 ) (8,499 ) Actuarial (gain) loss (1,387 ) (2,801 ) Effects of curtailment 573 — Settlement (2,496 ) (1,165 ) Foreign exchange (gain) loss 7,653 (3,309 ) Projected benefit obligation at December 31 158,466 131,416 Change in plan assets: Fair value of plan assets at January 1 91,471 76,042 Actual gain (loss) on plan assets 8,559 2,876 Employer contributions 28,073 25,114 Settlement (2,496 ) (1,165 ) Benefits paid (15,183 ) (8,499 ) Foreign exchange gain (loss) 5,301 (2,897 ) Fair value of plan assets at December 31 115,725 91,471 Funded status of the Plans at December 31 $ (42,741 ) $ (39,945 )
Schedule of Amounts Recognized in Balance Sheet	December 31, 2017 2016 (In thousands) Amounts recognized in the Consolidated Balance Sheets consist of: Prepaid benefit cost (included in non-current assets) $ 656 $ — Accrued benefit liability (included in pension and severance obligations) (43,397 ) (39,945 ) Net amount recognized at year end $ (42,741 ) $ (39,945 )
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	The following table summarizes, by component, the change in accumulated other comprehensive income (loss), net of tax related to our Plans: Prior Service Cost Actuarial Net Gain (Loss) Total (In thousands) Balance at December 31, 2015 $ 560 $ (1,985 ) $ (1,425 ) Amortization included in net periodic pension cost 22 73 95 Net gain (loss) arising during period — 2,468 2,468 Adjustments to unrealized components of defined benefit pension plan included in other comprehensive income (loss) 22 2,541 2,563 Balance at December 31, 2016 582 556 1,138 Amortization included in net periodic pension cost 21 69 90 Net gain (loss) arising during period — 5,075 5,075 Adjustments to unrealized components of defined benefit pension plan included in other comprehensive income (loss) 21 5,144 5,165 Balance at December 31, 2017 $ 603 $ 5,700 $ 6,303 Estimated amortization of cost to be included in 2018 net periodic pension cost $ 1 $ (147 ) $ (146 )
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	Information for pension plans with benefit obligations in excess of plan assets is as follows: December 31, 2017 2016 (In thousands) Plans with underfunded or non-funded projected benefit obligation: Aggregate projected benefit obligation $ 119,708 $ 131,416 Aggregate fair value of plan assets 76,313 91,471 Plans with underfunded or non-funded accumulated benefit obligation: Aggregate accumulated benefit obligation 53,720 49,285 Aggregate fair value of plan assets 18,970 16,811
Components of net periodic pension cost	The following table summarizes total pension expense: For the Year Ended December 31 2017 2016 2015 (In thousands) Components of net periodic pension cost and total pension expense: Service cost $ 33,823 $ 33,854 $ 12,481 Interest cost 4,067 3,641 2,954 Expected return on plan assets (4,537 ) (3,788 ) (3,330 ) Amortization of prior service cost 30 35 34 Recognized actuarial (gain) loss 84 94 91 Net periodic pension cost 33,467 33,836 12,230 Curtailment loss 574 — — Settlement (gain) loss 383 128 27 Total pension expense $ 34,424 $ 33,964 $ 12,257
Schedule of Assumptions Used	The following table summarizes the weighted-average assumptions used in computing the net periodic pension cost and projected benefit obligations: For the Year Ended December 31 2017 2016 2015 Discount rate for determining net periodic pension cost 3.1 % 3.3 % 4.2 % Discount rate for determining benefit obligations at December 31 3.2 % 3.1 % 3.3 % Rate of compensation increase for determining net periodic 3.8 % 3.9 % 4.7 % Rate of compensation increase for determining benefit obligations 3.8 % 3.8 % 3.9 % Expected rate of return on plan assets for determining net periodic 4.9 % 5.0 % 6.2 %
Schedule of Allocation of Plan Assets	The current rate of return assumption targets are based on asset allocation strategies as follows: Allocation Debt Equity Other Japan defined benefit plan 60 % 37 % 3 % Korea defined benefit plan 40 % 50 % 10 % Philippine defined benefit plan 40 % 56 % 4 % The fair value of our pension plan assets, by asset category utilizing the fair value hierarchy as discussed in Note 16 , is as follows: December 31, 2017 2016 (In thousands) Cash and cash equivalents (Level 1) $ 1,098 $ 10,419 Equity securities U.S. securities (Level 1) 16,854 12,602 Foreign securities (Level 1) 16,826 8,825 Foreign mutual funds (Level 1) 22,193 12,718 55,873 34,145 Debt securities U.S. government bonds (Level 1) 2,188 2,859 U.S. government bonds (Level 2) 830 — U.S. corporate bonds (Level 1) 2,144 1,980 U.S. corporate bonds (Level 2) 5 — Foreign government bonds (Level 1) 5,211 11,001 Foreign government bonds (Level 2) 6,270 7,727 Foreign corporate bonds (Level 1) 520 — Foreign corporate bonds (Level 2) 3,058 1,693 Foreign treasury notes (Level 1) 4,686 — Foreign mutual funds (Level 1) 8,787 10,044 33,699 35,304 Foreign guaranteed investment contracts (Level 2) 14,138 2,445 Taiwan retirement fund (Level 1) 10,094 8,972 Other (Level 1) 584 — Other (Level 2) 239 186 Total fair value of pension plan assets $ 115,725 $ 91,471
Schedule of Expected Benefit Payments	The estimated future benefit payments related to our foreign defined benefit plans are as follows: Payments (In thousands) 2018 $ 6,288 2019 7,516 2020 9,538 2021 11,602 2022 14,143 2023 to 2027 107,557

Accumulated Other Comprehensi42

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following table reflects the changes in accumulated other comprehensive income (loss), net of tax: Defined Benefit Pension Foreign Currency Translation Total (In thousands) Balance at December 31, 2015 $ (1,425 ) $ (659 ) $ (2,084 ) Other comprehensive income (loss) before reclassifications 2,468 5,783 8,251 Amounts reclassified from accumulated other comprehensive income (loss) 95 — 95 Other comprehensive income (loss) 2,563 5,783 8,346 Balance at December 31, 2016 $ 1,138 $ 5,124 $ 6,262 Other comprehensive income (loss) before reclassifications 5,075 11,092 16,167 Amounts reclassified from accumulated other comprehensive income (loss) 90 — 90 Other comprehensive income (loss) 5,165 11,092 16,257 Balance at December 31, 2017 $ 6,303 $ 16,216 $ 22,519

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Valuation of money market funds and restricted cash using quoted market prices in active markets for identical assets	Recurring fair value measurements consist of the following: December 31, 2017 2016 (In thousands) Cash equivalent money market funds (Level 1) $ 121,627 $ 39,548 Restricted cash money market funds (Level 1) 2,000 2,000
Financial instruments that are not recorded at fair value	The following table presents the fair value of financial instruments that are not recorded at fair value on a recurring basis: December 31, 2017 December 31, 2016 Fair Value Carrying Value Fair Value Carrying Value (In thousands) Senior notes (Level 1) $ 745,943 $ 723,867 $ 954,765 $ 922,140 Revolving credit facilities and term loans (Level 2) 639,689 640,562 551,793 552,690 Total financial instruments $ 1,385,632 $ 1,364,429 $ 1,506,558 $ 1,474,830

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Future minimum lease payments under operating leases that have initial or remaining noncancelable lease terms in excess of one year are: For the Year Ended December 31 (In thousands) 2018 $ 26,439 2019 21,740 2020 13,694 2021 10,530 2022 8,468 Thereafter 28,955 Total future minimum lease payments $ 109,826

Business Segments, Customer C45

Business Segments, Customer Concentrations and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Revenue from External Customers by Products and Services	Net sales by product group consist of the following: For the Year Ended December 31, 2017 2016 2015 (In thousands) Advanced Products $ 1,950,340 $ 1,679,529 $ 1,432,493 Mainstream Products 2,236,157 2,214,106 1,452,110 Total net sales $ 4,186,497 $ 3,893,635 $ 2,884,603
Net sales by country, and property, plant and equipment by physical location	Net sales by region based on customer headquarters location consist of the following: For the Year Ended December 31, 2017 2016 2015 (In thousands) Japan $ 1,208,822 $ 1,158,318 $ 372,810 Asia Pacific (excluding Japan) 827,061 627,177 609,409 Europe, Middle East and Africa 536,552 487,584 489,842 Total foreign countries 2,572,435 2,273,079 1,472,061 United States 1,614,062 1,620,556 1,412,542 Total net sales $ 4,186,497 $ 3,893,635 $ 2,884,603
Schedule of Disclosure on Geographic Areas, Long-Lived Assets in Individual Foreign Countries by Country	Property, plant and equipment, net, based on physical location, consist of the following: December 31, 2017 2016 (In thousands) China $ 528,739 $ 500,319 Japan 246,223 245,233 Korea 1,131,271 1,130,147 Malaysia 47,922 36,248 Philippines 309,425 313,885 Portugal 64,578 — Taiwan 356,174 326,614 Other foreign countries 216 243 Total foreign countries 2,684,548 2,552,689 United States 10,517 11,959 Total property, plant and equipment, net $ 2,695,065 $ 2,564,648

Quarterly Results (Unaudited) (

Quarterly Results (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	The following table sets forth our consolidated unaudited financial data for the last eight quarters ended December 31, 2017 . We believe that we have included all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of our selected quarterly data. The calculation of basic and diluted per share amounts for each quarter is based on the weighted-average shares outstanding for that period; consequently, the sum of the quarters may not necessarily be equal to the full year basic and diluted net income per share. For the Quarter Ended Dec. 31, 2017 (c) Sept. 30, 2017 June 30, 2017 (a) Mar. 31, 2017 Dec. 31, 2016 Sept. 30, 2016 June 30, 2016 Mar. 31, 2016 (In thousands, except per share data) Net sales $ 1,148,423 $ 1,135,027 $ 989,447 $ 913,600 $ 1,021,613 $ 1,086,014 $ 917,326 $ 868,682 Gross profit 225,494 216,638 172,235 142,906 227,187 213,800 131,606 122,884 Operating income (b) 110,128 98,237 168,293 24,655 126,689 114,615 30,542 22,094 Income tax (benefit) expense (12,782 ) 18,752 32,573 439 18,534 24,086 3,360 1,873 Net income (loss) 101,943 55,630 116,459 (9,144 ) 101,202 61,141 5,366 (405 ) Net income (loss) attributable to Amkor 100,770 54,435 115,507 (10,006 ) 100,263 60,089 4,713 (875 ) Net income (loss) attributable to Amkor per common share: Basic $ 0.42 $ 0.23 $ 0.48 $ (0.04 ) $ 0.42 $ 0.25 $ 0.02 $ — Diluted $ 0.42 $ 0.23 $ 0.48 $ (0.04 ) $ 0.42 $ 0.25 $ 0.02 $ — (a) In May 2017, we completed the purchase of Nanium. Nanium's financial results have been included in our Consolidated Financial Statements from the date of acquisition. (b) In May 2017, we sold the land and buildings comprising our K1 factory for $142.4 million which resulted in a pre-tax gain of $108.1 million . (c) In the fourth quarter of 2017, net income includes an estimated net tax benefit of $41.6 million primarily due to the reversal of a valuation allowance on certain U.S. deferred tax assets as a result of the enactment of the Tax Act.

Description of Business and S47

Description of Business and Summary of Significant Accounting Policies (Variable Interest Entity) (Details) - Variable Interest Entity, Primary Beneficiary $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Variable Interest Entity [Line Items]
Ownership Percentage	40.00%
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 16.9
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ 0.4

Description of Business and S48

Description of Business and Summary of Significant Accounting Policies (Other) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 30, 2015
Land use rights | Minimum
Summary of Significant Accounting Policies [Line Items]
Useful life	50 years
Land use rights | Maximum
Summary of Significant Accounting Policies [Line Items]
Useful life	90 years
Buildings and improvements | Minimum
Summary of Significant Accounting Policies [Line Items]
Useful life	10 years
Buildings and improvements | Maximum
Summary of Significant Accounting Policies [Line Items]
Useful life	40 years
Machinery and equipment | Minimum
Summary of Significant Accounting Policies [Line Items]
Useful life	2 years
Machinery and equipment | Maximum
Summary of Significant Accounting Policies [Line Items]
Useful life	7 years
Software and computer equipment | Minimum
Summary of Significant Accounting Policies [Line Items]
Useful life	3 years
Software and computer equipment | Maximum
Summary of Significant Accounting Policies [Line Items]
Useful life	5 years
Furniture, fixtures and other equipment | Minimum
Summary of Significant Accounting Policies [Line Items]
Useful life	4 years
Furniture, fixtures and other equipment | Maximum
Summary of Significant Accounting Policies [Line Items]
Useful life	10 years
J-Devices
Summary of Significant Accounting Policies [Line Items]
Ownership interest in acquiree (percent)		100.00%
J-Devices
Summary of Significant Accounting Policies [Line Items]
Ownership interest in acquiree (percent)		100.00%

New Accounting Standards Adjust

New Accounting Standards Adjustment for new accounting pronouncement (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement:
Net sales	$ 1,148,423	$ 1,135,027	$ 989,447	$ 913,600	$ 1,021,613	$ 1,086,014	$ 917,326	$ 868,682	$ 4,186,497	$ 3,893,635	$ 2,884,603
Cost of sales									3,429,224	3,198,158	2,405,338
Net income	$ 101,943	$ 55,630	$ 116,459	$ (9,144)	$ 101,202	$ 61,141	$ 5,366	$ (405)	$ 264,888	$ 167,304	$ 53,893
Basic (in dollars per share)	$ 0.42	$ 0.23	$ 0.48	$ (0.04)	$ 0.42	$ 0.25	$ 0.02	$ 0	$ 1.09	$ 0.69	$ 0.22
Diluted (in dollars per share)	$ 0.42	$ 0.23	$ 0.48	$ (0.04)	$ 0.42	$ 0.25	$ 0.02	$ 0	$ 1.09	$ 0.69	$ 0.22
Balance Sheet:
Accounts receivable, net	$ 692,287				$ 563,107				$ 692,287	$ 563,107
Inventories	326,492				267,990				326,492	267,990
Accrued expenses	374,598				338,669				374,598	338,669
(Accumulated deficit) retained earnings	(42,851)				$ (303,557)				(42,851)	(303,557)
New Revenue Standard Adjustment (Estimate) | Accounting Standards Update 2014-09
Income Statement:
Net sales									24,000	36,000
Cost of sales									17,000	21,000
Net income									$ 5,000	$ 11,000
Basic (in dollars per share)									$ 0.02	$ 0.05
Diluted (in dollars per share)									$ 0.02	$ 0.04
Balance Sheet:
Accounts receivable, net	106,000								$ 106,000
Inventories	(113,000)								(113,000)
Accrued expenses	(48,000)								(48,000)
(Accumulated deficit) retained earnings	31,000								31,000
As Adjusted (Estimate) | Accounting Standards Update 2014-09
Income Statement:
Net sales									4,210,497	$ 3,929,635
Cost of sales									3,446,224	3,219,158
Net income									$ 269,888	$ 178,304
Basic (in dollars per share)									$ 1.11	$ 0.74
Diluted (in dollars per share)									$ 1.11	$ 0.73
Balance Sheet:
Accounts receivable, net	798,287								$ 798,287
Inventories	213,492								213,492
Accrued expenses	326,598								326,598
(Accumulated deficit) retained earnings	$ (11,851)								$ (11,851)

Acquisitions (Step Acquisition

Acquisitions (Step Acquisition of J-Devices) (Details) - USD ($) $ in Thousands	Dec. 30, 2015	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 22, 2017	Dec. 29, 2015
Business Acquisition [Line Items]
Payments to acquire investment			$ 0	$ 0	$ 12,908
J-Devices
Business Acquisition [Line Items]
Ownership Interest (percent)							65.70%
Ownership interest in acquiree (percent)	100.00%
Nanium
Business Acquisition [Line Items]
Ownership interest acquired (as a percent)						100.00%
J-Devices
Business Acquisition [Line Items]
Ownership interest in acquiree (percent)	100.00%
Payments to acquire investment	$ 105,400
Equity interest fair value remeasurement gain		$ 16,100
Business combination, step acquisition, foreign currency translation gain (loss)		(29,600)
Gain (loss) from acquisition of J-Devices		$ (13,500)

Acquisitions (Consideration Tra

Acquisitions (Consideration Transferred and Identifiable Assets and Liabilities Assumed) (Details) - USD ($) $ in Thousands	Dec. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Recognized amounts of identifiable assets acquired and liabilities assumed:
Goodwill		$ 25,036	$ 24,122	$ 23,409
J-Devices
Fair value of consideration transferred:
Cash	$ 105,391
Fair value of our previously held equity interest in J-Devices	160,087
Total	265,478
Recognized amounts of identifiable assets acquired and liabilities assumed:
Cash	127,968
Accounts receivable	180,177
Inventory	42,502
Other current assets	2,363
Property, plant and equipment	230,319
Other assets	9,268
Short-term borrowings and current portion of long-term debt	(36,770)
Other current liabilities	(251,405)
Long-term debt	(18,885)
Pension obligations	(22,250)
Other non-current liabilities	(21,218)
Total identifiable net assets	242,069
Goodwill	23,409
Total	$ 265,478

Acquisitions Pro forma consolid

Acquisitions Pro forma consolidated operating results, nonrecurring activities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Japanese Subsidiary
Business Acquisition, Pro Forma Information, Nonrecurring Activities [Line Items]
Reversal of deferred tax asset valuation allowance	$ 16.2
Gain on foreign currency translation adjustment	12.6
J-Devices
Business Acquisition, Pro Forma Information, Nonrecurring Activities [Line Items]
Business combination, pro forma adjustment, net gain (loss)	$ (13.5)

Acquisitions (Pro Forma Consoli

Acquisitions (Pro Forma Consolidated Results of Operations - J-Devices) (Details) - J-Devices - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Net sales	$ 3,696,495	$ 4,051,076
Net income	88,190	153,049
Net income attributable to Amkor	$ 85,394	$ 149,548
Basic earnings per share	$ 0.36	$ 0.65
Diluted earnings per share	$ 0.36	$ 0.63

Share-Based Compensation Plan54

Share-Based Compensation Plans (Stock Options) (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares Outstanding beginning balance | shares	2,443
Number of Shares Granted | shares	2,900
Number of Shares Exercised | shares	(469)
Number of Shares Forfeited or expired | shares	(122)
Number of Shares Outstanding ending balance | shares	4,752
Number of Shares Fully vested and expected to vest | shares	4,632
Number of Shares Exercisable | shares	1,733
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price Per Share Outstanding beginning balance (in dollars per share) | $ / shares	$ 6.93
Weighted Average Exercise Price Per Share Granted (in dollars per share) | $ / shares	9.97
Weighted Average Exercise Price Per Share Exercised (in dollars per share) | $ / shares	6.66
Weighted Average Exercise Price Per Share Forfeited or expired (in dollars per share) | $ / shares	5.12
Weighted Average Exercise Price Per Share Outstanding ending balance (in dollars per share) | $ / shares	8.86
Weighted Average Exercise Price Per Share Fully vested and expected to vest (in dollars per share) | $ / shares	8.83
Weighted Average Exercise Price Per Share Exercisable (in dollars per share) | $ / shares	$ 7.17
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Term Outstanding (years)	7 years 6 months 3 days
Average Remaining Contractual Term Fully vested and expected to vest (years)	7 years 5 months 16 days
Average Remaining Contractual Term Exercisable (years)	4 years 9 months
Aggregate intrinsic value Outstanding ending balance (in dollars) | $	$ 6,403
Aggregate intrinsic value Fully vested and expected to vest (in dollars) | $	6,369
Aggregate intrinsic value Exercisable (in dollars) | $	$ 5,455

Share-Based Compensation Plan55

Share-Based Compensation Plans (Weighted Average Fair Value) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected life (in years)	5 years 7 months 28 days	6 years 5 months 13 days	5 years 10 months 6 days
Risk-free interest rate	1.90%	1.50%	1.80%
Volatility	43.00%	48.00%	45.00%
Dividend yield	0.00%	0.00%	0.00%
Weighted-average grant date fair value per option granted	$ 4.24	$ 2.89	$ 3.14

Share-Based Compensation Plan56

Share-Based Compensation Plans (Restricted Shares) (Details) - Restricted shares shares in Thousands	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Number of Shares Nonvested beginning balance | shares	145
Number of Shares Awards granted | shares	224
Number of Shares Awards vested | shares	(181)
Number of Shares Awards forfeited | shares	0
Number of Shares Nonvested ending balance | shares	188
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Grant-Date Fair Value Nonvested beginning balance (in dollars per share) | $ / shares	$ 5.02
Weighted Average Grant-Date Fair Value Awards granted (in dollars per share) | $ / shares	10.06
Weighted Average Grant-Date Fair Value Awards vested (in dollars per share) | $ / shares	5.93
Weighted Average Grant-Date Fair Value Awards forfeited (in dollars per share) | $ / shares	0
Weighted Average Grant-Date Fair Value Nonvested ending balance (in dollars per share) | $ / shares	$ 10.15

Share-Based Compensation Plan57

Share-Based Compensation Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 02, 2008
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 5,145	$ 3,251	$ 3,852
Deferred income tax benefits for stock options and restricted stock	$ 2,400	$ 0	$ 0
2007 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)				17,000,000
Number of shares available for grant (in shares)	8,000,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Unrecognized compensation expense from Restricted Stock	$ 9,600
Weighted-average period of recognition of unrecognized compensation expense	2 years 11 months 13 days
Stock Options | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Stock Options | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Unrecognized compensation expense from Restricted Stock	$ 1,500
Weighted-average period of recognition of unrecognized compensation expense	2 years 9 months 18 days
Restricted shares vesting (as a percent)	6.25%
Restricted shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares vesting (as a percent)	100.00%
Director | Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year

Other Income and Expense (Detai

Other Income and Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income and Expenses [Abstract]
Interest income	$ (3,215)	$ (1,326)	$ (2,539)
Foreign currency (gain) loss, net	11,823	(3,592)	(7,849)
Loss on debt retirement	4,835	0	9,560
Loss from acquisition of J-Devices (Note 3)	0	0	13,501
Other (income) expense, net	(1,554)	(936)	(2,122)
Total other (income) expense, net	$ 11,889	$ (5,854)	$ 10,551

Income Taxes (Effects of Tax Re

Income Taxes (Effects of Tax Reform) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Toll charge before credits	$ 162,750
Tax credits	(128,395)
Remeasure deferred tax assets	36,794
Reverse valuation allowance	(112,703)
Total impact of U.S. tax reform	$ (41,554)	$ 0	$ 0

Income Taxes (Components of inc

Income Taxes (Components of income tax expense and income before taxes, by jurisdiction) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Geographic sources of income (loss) before income taxes
United States									$ 14,935	$ (12,385)	$ (39,684)
Foreign									288,935	227,542	107,596
Income before taxes and equity in earnings of unconsolidated affiliate									303,870	215,157	67,912
Current:
Federal									0	0	0
State									11	22	11
Foreign									81,969	49,577	28,721
Current income tax expense (benefit)									81,980	49,599	28,732
Deferred:
Federal									(36,943)	0	0
State									(4,611)	0	0
Foreign									(1,444)	(1,746)	(697)
Deferred income tax expense (benefit)									(42,998)	(1,746)	(697)
Income tax expense	$ (12,782)	$ 18,752	$ 32,573	$ 439	$ 18,534	$ 24,086	$ 3,360	$ 1,873	$ 38,982	$ 47,853	$ 28,035

Income Taxes (Reconciliation of

Income Taxes (Reconciliation of effective tax rate) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory income tax rate (in dollars per share)									35.00%	35.00%	35.00%
Reconciliation between statutory rate and income tax provision
U.S. federal tax at 35%									$ 106,354	$ 75,305	$ 23,769
State taxes, net of federal benefit									2,193	836	2,622
Foreign income taxed at different rates									(51,412)	(17,907)	(11,756)
Foreign exchange (loss) gain									29,756	(1,127)	(5,680)
Change in valuation allowance									(4,703)	(7,362)	18,259
Adjustments related to prior years									3,329	(2,648)	(912)
U.S. tax reform (the Tax Act)									(41,554)	0	0
Income tax credits generated									(7,296)	(40,301)	(1,919)
Repatriation of foreign earnings and profits									719	25,604	91
Expiration of net operating losses and credits									166	15,092	74
Non-deductible loss on acquisition of J-Devices (Note 3)									0	0	4,725
Other									1,430	361	(1,238)
Income tax expense	$ (12,782)	$ 18,752	$ 32,573	$ 439	$ 18,534	$ 24,086	$ 3,360	$ 1,873	$ 38,982	$ 47,853	$ 28,035

Income Taxes (Components of def

Income Taxes (Components of deferred tax assets and liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Components of Deferred Tax Assets and Liabilities [Abstract]
Net operating loss carryforwards	$ 53,130	$ 111,899
Income tax credits	23,998	41,900
Property, plant and equipment	35,479	21,860
Accrued liabilities	68,091	68,563
Receivable	32,719	0
Unrealized foreign exchange loss	1,924	531
Other	12,682	14,583
Total deferred tax assets	228,023	259,336
Valuation allowance	(83,338)	(165,367)
Total deferred tax assets net of valuation allowance	144,685	93,969
Property, plant and equipment	15,754	20,407
Deferred gain	939	2,655
Unrealized foreign exchange gain	8,383	990
Other	4,566	4,836
Total deferred tax liabilities	29,642	28,888
Other assets	117,608	66,831
Other non-current liabilities	(2,565)	(1,750)
Net deferred tax assets	$ 115,043	$ 65,081

Income Taxes (Tax holidays) (De

Income Taxes (Tax holidays) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax benefit from income tax holiday	$ 6.2	$ 5.6	$ 3.3
Benefit from income tax holiday on diluted earnings per share (in dollars per share)	$ 0.03	$ 0.02	$ 0.01

Income Taxes (Valuation allowan

Income Taxes (Valuation allowance) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance [Line Items]
Total valuation allowance	$ 83,338	$ 165,367
United States
Valuation Allowance [Line Items]
Total valuation allowance	43,719	164,479
Portugal
Valuation Allowance [Line Items]
Total valuation allowance	39,009	0
Other
Valuation Allowance [Line Items]
Total valuation allowance	$ 610	$ 888

Income Taxes (Net operating los

Income Taxes (Net operating loss carryforwards) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Loss Carryforwards and other details [Abstract]
Undistributed earnings of foreign subsidiaries	$ 1,100,000
U.S. Federal
Loss Carryforwards and other details [Abstract]
Operating loss carryforwards	220,445	$ 292,715
Tax credit carryforward	12,600
U.S. State
Loss Carryforwards and other details [Abstract]
Operating loss carryforwards	121,095	138,218
Foreign
Loss Carryforwards and other details [Abstract]
Operating loss carryforwards	2,967	$ 3,378
Repatriation of earnings estimated tax impact	$ 80,500

Income Taxes (Unrecognized tax

Income Taxes (Unrecognized tax benefits - rollforward and discussion) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, beginning of period	$ 23,149	$ 23,332	$ 12,670
Additions based on tax positions related to the current year	1,419	1,822	12,727
Additions for tax positions of prior years	2,661	689	3,341
Reductions for tax positions of prior years	(1)	(2,589)	(4,815)
Reductions from lapse of statutes of limitations	(17)	(105)	(591)
Balance, end of period	27,211	$ 23,149	$ 23,332
Income tax contingency [Abstract]
Unrecognized tax benefits, period increase (decrease)	4,100
Liability for uncertain tax positions	24,800
Accrued and unpaid interest and penalties	$ 4,200

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dilutive Securities Adjustments [Line Items]
Net income attributable to Amkor	$ 100,770	$ 54,435	$ 115,507	$ (10,006)	$ 100,263	$ 60,089	$ 4,713	$ (875)	$ 260,706	$ 164,190	$ 51,098
Income allocated to participating securities									0	0	(59)
Net income available to Amkor common stockholders									$ 260,706	$ 164,190	$ 51,039
Weighted-average shares outstanding — basic									238,937	237,416	236,850
Effect of dilutive securities:
Weighted-average shares outstanding — diluted									239,651	238,034	237,170
Net income attributable to Amkor per common share:
Basic (in dollars per share)	$ 0.42	$ 0.23	$ 0.48	$ (0.04)	$ 0.42	$ 0.25	$ 0.02	$ 0	$ 1.09	$ 0.69	$ 0.22
Diluted (in dollars per share)	$ 0.42	$ 0.23	$ 0.48	$ (0.04)	$ 0.42	$ 0.25	$ 0.02	$ 0	$ 1.09	$ 0.69	$ 0.22
Stock Options and Restricted Share Awards [Member]
Effect of dilutive securities:
Stock options and restricted share awards									714	618	320

Earnings Per Share (Antidilutiv

Earnings Per Share (Antidilutive) (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock Options And Restricted Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options and restricted share awards	3,445	1,135	1,858

Factoring of Accounts Receiva69

Factoring of Accounts Receivable Factoring of Accounts Receivable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Total Factored
Factoring of Accounts Receivable [Line Items]
Accounts Receivable Sold without Recourse	$ 611.2	$ 574.1
Factoring Fees
Factoring of Accounts Receivable [Line Items]
Accounts Receivable Sold without Recourse	$ 4.6	$ 2.5

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventories
Raw materials and purchased components	$ 213,649	$ 173,035
Work-in-process	112,843	94,955
Total inventories	$ 326,492	$ 267,990

Property, Plant and Equipment71

Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 6,896,008	$ 6,427,413
Less accumulated depreciation and amortization	(4,200,943)	(3,862,765)
Total property, plant and equipment, net	2,695,065	2,564,648
Depreciation expense	580,172	552,989	$ 492,458
Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	224,894	240,719
Land use rights
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	26,845	26,845
Buildings and improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	1,384,846	1,362,007
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	4,938,291	4,483,523
Software and computer equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	200,500	205,969
Furniture, fixtures and other equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	15,722	21,313
Construction in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 104,910	$ 87,037

Property, Plant and Equipment72

Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	May 31, 2017	Nov. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 6,896,008	$ 6,427,413
Proceeds from sale of property, plant and equipment			141,530	45,635	$ 6,945
Gain on sale K1 factory			2,648	(1,390)	$ (1,190)
Korea
Property, Plant and Equipment [Line Items]
Proceeds from sale of property, plant and equipment	$ 142,400	$ 142,400
Percentage of proceeds received		10.00%
Gain on sale K1 factory	$ 108,100	$ 108,100
Construction in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			104,910	87,037
Construction in progress | K5 Facility | Korea
Property, Plant and Equipment [Line Items]
Total property, plant and equipment			$ 46,900	$ 44,800

Goodwill (Details)

Goodwill (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 30, 2015
Goodwill [Roll Forward]
Beginning Balance	$ 24,122,000	$ 23,409,000
Goodwill acquired		713,000
Translation adjustment	914,000
Ending Balance	25,036,000	24,122,000
Goodwill impairment	$ 0	$ 0
J-Devices
Goodwill [Roll Forward]
Ownership interest in J-Devices (percent)			100.00%

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Payroll and benefits	$ 134,785	$ 117,636
Deferred revenue and customer advances	63,196	65,653
Income taxes payable	56,664	37,961
Accrued settlement costs	37,783	35,304
Accrued severance plan obligations (Note 14)	15,190	14,053
Accrued interest	11,873	13,046
Other accrued expenses	55,107	55,016
Total accrued expenses	$ 374,598	$ 338,669

Debt (Long Term Debt) (Details)

Debt (Long Term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	May 30, 2017	Apr. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total debt	$ 1,365,533			$ 1,477,661
Less: Unamortized premium and deferred debt costs, net	(1,104)			(2,831)
Less: Short-term borrowings and current portion of long-term debt	(123,848)			(35,192)
Long-term debt (including related party)	1,240,581			1,439,638
$200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019 | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Total debt	0			0
6.625% Senior notes, due June 2021 | Senior notes
Debt Instrument [Line Items]
Total debt	200,000			400,000
6.375% Senior notes, due October 2022 | Senior notes
Debt Instrument [Line Items]
Total debt	524,971			524,971
Korea | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due June 2018 | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Total debt	75,000		$ 100,000	0
Korea | Term loan, LIBOR plus 2.70%, due December 2019 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	55,000			55,000
Korea | Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	150,000			150,000
Korea | Term loan, fixed rate at 3.70%, due May 2020 | Term Loan
Debt Instrument [Line Items]
Total debt	120,000	$ 120,000		0
Korea | Term loan, fund floating rate plus 1.60%, due June 2020 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	86,000			86,000
Korea | Term loan, LIBOR plus 2.60%, due May 2018 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	0			120,000
Korea | Term loan, foreign currency funding-linked base rate plus 1.33%, due May 2020 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	0			80,000
Japan | Short-term term loans, variable rates | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Total debt	30,455			22,230
Japan | Term loans, fixed rate at 0.53%, due April 2018 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	6,744			19,460
Japan | Term loan, fixed rate at 0.86% due June 2022 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	39,933			0
Japan | Term loan, fixed rate at 0.60% due July 2022 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	8,430			0
Taiwan | Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 (Taiwan) | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Total debt	20,000			20,000
China | Term loan, LIBOR plus 1.80% due December 2019 | Loans Payable
Debt Instrument [Line Items]
Total debt	$ 49,000			$ 0

Debt (Additional Information) (

Debt (Additional Information) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Apr. 30, 2017
Subsidiary Term Loans | Korea | Term loan, LIBOR plus 2.70%, due December 2019
Debt Instrument [Line Items]
Interest rate spread (as a percent)	2.70%
Subsidiary Term Loans | Korea | Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020
Debt Instrument [Line Items]
Interest rate spread (as a percent)	1.32%
Subsidiary Term Loans | Korea | Term loan, fund floating rate plus 1.60%, due June 2020
Debt Instrument [Line Items]
Interest rate spread (as a percent)	1.60%
Subsidiary Term Loans | Korea | Term loan, LIBOR plus 2.60%, due May 2018
Debt Instrument [Line Items]
Interest rate spread (as a percent)	2.60%
Subsidiary Term Loans | Japan | Term loans, fixed rate at 0.53%, due April 2018
Debt Instrument [Line Items]
Interest rate (as a percent)	0.53%
Subsidiary Term Loans | Japan | Term loan, fixed rate at 0.86% due June 2022
Debt Instrument [Line Items]
Interest rate (as a percent)	0.86%
Subsidiary Term Loans | Japan | Term loan, fixed rate at 0.60% due July 2022
Debt Instrument [Line Items]
Interest rate (as a percent)	0.60%
Term Loan | Korea | Term loan, fixed rate at 3.70%, due May 2020
Debt Instrument [Line Items]
Interest rate (as a percent)	3.70%
Senior notes | 6.625% Senior notes, due June 2021
Debt Instrument [Line Items]
Interest rate (as a percent)	6.625%
Senior notes | 6.375% Senior notes, due October 2022
Debt Instrument [Line Items]
Interest rate (as a percent)	6.375%
Revolving Credit Facility | Line of Credit | $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019
Debt Instrument [Line Items]
Credit facility, borrowing capacity	$ 200,000,000
Revolving Credit Facility | Line of Credit | $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019 | Minimum
Debt Instrument [Line Items]
Interest rate (as a percent)	1.25%
Revolving Credit Facility | Line of Credit | $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019 | Maximum
Debt Instrument [Line Items]
Interest rate (as a percent)	1.75%
Revolving Credit Facility | Line of Credit | Korea | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due June 2018
Debt Instrument [Line Items]
Credit facility, borrowing capacity	$ 75,000,000	$ 75,000,000
Interest rate spread (as a percent)	1.60%
Base Rate | Subsidiary Term Loans | Korea | Term loan, foreign currency funding-linked base rate plus 1.33%, due May 2020
Debt Instrument [Line Items]
Interest rate spread (as a percent)	1.33%
London Interbank Offered Rate (LIBOR) | Loans Payable | China | Term loan, LIBOR plus 1.80% due December 2019
Debt Instrument [Line Items]
Interest rate spread (as a percent)	1.80%

Debt (Narrative) (Details)

Debt (Narrative) (Details)	1 Months Ended					12 Months Ended
	Jul. 31, 2017USD ($)	Jul. 31, 2017JPY (¥)	Jun. 30, 2017JPY (¥)	Apr. 30, 2017USD ($)	Jan. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Jul. 31, 2017JPY (¥)	May 30, 2017USD ($)	Nov. 30, 2015USD ($)	May 31, 2015USD ($)
Debt Instruments [Abstract]
Total debt						$ 1,365,533,000	$ 1,477,661,000
Long-term debt, related party						0	75,000,000
Proceeds from revolving credit facilities						75,000,000	125,000,000	$ 290,000,000
Proceeds from issuance of long-term debt						223,976,000	46,000,000	$ 400,000,000
China | Term loan, LIBOR plus 1.80% due December 2019
Debt Instruments [Abstract]
Periodic payment amount						500,000
Letter of Credit | $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019
Debt Instruments [Abstract]
Credit facility, borrowing capacity						25,000,000
Senior notes | 6.625% Senior notes, due June 2021
Debt Instruments [Abstract]
Extinguishment of debt	$ 200,000,000
Total debt						$ 200,000,000	400,000,000
Interest rate (as a percent)						6.625%
Due to related parties, current	$ 17,500,000
Redemption price (as a percent)	101.656%	101.656%
Payments for retirement of debt	$ 3,300,000
Write off of deferred debt issuance cost	$ 1,100,000
Line of Credit | Revolving Credit Facility | $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019
Debt Instruments [Abstract]
Credit facility, borrowing capacity						$ 200,000,000
Remaining borrowing capacity						199,400,000
Total debt						0	0
Line of Credit | Revolving Credit Facility | Korea | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due June 2018
Debt Instruments [Abstract]
Credit facility, borrowing capacity				$ 75,000,000		75,000,000
Total debt				100,000,000		75,000,000	0
Proceeds from revolving credit facilities				75,000,000
Line of Credit | Revolving Credit Facility | Japan | Short-term term loans, variable rates
Debt Instruments [Abstract]
Total debt						30,455,000	22,230,000
Line of Credit | Revolving Credit Facility | Taiwan | Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 (Taiwan)
Debt Instruments [Abstract]
Credit facility, borrowing capacity											$ 39,000,000
Remaining borrowing capacity						19,000,000
Total debt						20,000,000	20,000,000
Line of Credit | Letter of Credit | $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019
Debt Instruments [Abstract]
Letter of credit						600,000
Term Loan | Korea | Term loan, foreign currency funding-linked base rate plus 1.33%, due May 2020
Debt Instruments [Abstract]
Repayments of debt				$ 80,000,000
Term Loan | Korea | Term loan, fixed rate at 3.70%, due May 2020
Debt Instruments [Abstract]
Total debt						$ 120,000,000	0			$ 120,000,000
Interest rate (as a percent)						3.70%
Subsidiary Term Loans | Korea | Term loan, foreign currency funding-linked base rate plus 1.33%, due May 2020
Debt Instruments [Abstract]
Total debt						$ 0	80,000,000
Subsidiary Term Loans | Korea | Term loan, LIBOR plus 2.60%, due May 2018
Debt Instruments [Abstract]
Total debt						0	120,000,000
Subsidiary Term Loans | Korea | Term loan, fund floating rate plus 1.60%, due June 2020
Debt Instruments [Abstract]
Total debt						86,000,000	86,000,000
Unused borrowing capacity						64,000,000						$ 150,000,000
Subsidiary Term Loans | Japan | Short-term term loans, variable rates
Debt Instruments [Abstract]
Remaining borrowing capacity						6,200,000
Subsidiary Term Loans | Japan | Term loan, fixed rate at 0.86% due June 2022
Debt Instruments [Abstract]
Total debt						$ 39,933,000	0
Interest rate (as a percent)						0.86%
Amount of debt agreement | ¥			¥ 5,000,000,000
Periodic payment amount | ¥			250,000,000
Proceeds from issuance of long-term debt | ¥			¥ 5,000,000,000
Subsidiary Term Loans | Japan | Term loan, fixed rate at 0.60% due July 2022
Debt Instruments [Abstract]
Total debt						$ 8,430,000	0
Interest rate (as a percent)						0.60%
Amount of debt agreement | ¥									¥ 1,000,000,000
Periodic payment amount | ¥		¥ 50,000,000
Proceeds from issuance of long-term debt | ¥		¥ 1,000,000,000
Loans Payable | China | Term loan, LIBOR plus 1.80% due December 2019
Debt Instruments [Abstract]
Total debt						$ 49,000,000	$ 0
Amount of debt agreement						$ 50,000,000
Proceeds from issuance of long-term debt					$ 50,000,000

Debt (Interest Rates) (Details)

Debt (Interest Rates) (Details)	Dec. 31, 2017	Dec. 31, 2016
Subsidiary Term Loans | Term loan, LIBOR plus 2.60%, due May 2018 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	3.49%
Subsidiary Term Loans | Term loan, LIBOR plus 2.70%, due December 2019 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	4.02%	3.54%
Subsidiary Term Loans | Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	4.06%	3.58%
Subsidiary Term Loans | Term loan, foreign currency funding-linked base rate plus 1.33%, due May 2020 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	3.59%
Subsidiary Term Loans | Term loan, fund floating rate plus 1.60%, due June 2020 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	3.29%	2.79%
Loans Payable | Term loan, LIBOR plus 1.80% due December 2019 | China
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	3.16%	0.00%
Revolving Credit Facility | Line of Credit | $200 million revolving credit facility, LIBOR plus 1.25%-1.75%, due December 2019
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	0.00%
Revolving Credit Facility | Line of Credit | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due June 2018 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	4.01%	0.00%
Revolving Credit Facility | Line of Credit | Short-term term loans, variable rates | Japan
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.22%	0.32%
Revolving Credit Facility | Line of Credit | Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 (Taiwan) | Taiwan
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	3.18%	2.78%

Debt (Maturities) (Details)

Debt (Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
2,018	$ 123,848
2,019	173,649
2,020	326,649
2,021	210,649
2,022	530,738
Total debt	$ 1,365,533	$ 1,477,661

Pension and Severance Plans (Ko

Pension and Severance Plans (Korean Severance Plan) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Liability, Current and Noncurrent [Roll Forward]
Total accrued severance plan obligations at December 31	$ 153,735	$ 136,214	$ 142,959
Less current portion of accrued severance plan obligations (Note 12)	15,190	14,053	14,306
Non-current portion of accrued severance plan obligations	138,545	122,161	128,653
Korean Severance Plan
Deferred Compensation Liability, Current and Noncurrent [Roll Forward]
Balance at January 1	136,396	143,151	146,880
Provision of severance benefits	11,714	6,746	21,088
Severance payments	(11,787)	(9,429)	(15,021)
Foreign currency (gain) loss	17,597	(4,072)	(9,796)
Balance at the end of year	153,920	136,396	143,151
Payments remaining with the National Pension Fund	$ (185)	$ (182)	$ (192)

Pension and Severance Plans (De

Pension and Severance Plans (Defined Benefit Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in projected benefit obligation:
Projected benefit obligation at January 1	$ 131,416	$ 109,695
Service cost	33,823	33,854	$ 12,481
Interest cost	4,067	3,641	2,954
Benefits paid	(15,183)	(8,499)
Actuarial (gain) loss	(1,387)	(2,801)
Effects of curtailment	(573)	0
Settlement	(2,496)	(1,165)
Foreign exchange (gain) loss	7,653	(3,309)
Projected benefit obligation at December 31	158,466	131,416	109,695
Change in plan assets:
Fair value of plan assets at January 1	91,471	76,042
Actual gain (loss) on plan assets	8,559	2,876
Employer contributions	28,073	25,114
Settlement	(2,496)	(1,165)
Benefits paid	(15,183)	(8,499)
Foreign exchange gain (loss)	5,301	(2,897)
Fair value of plan assets at December 31	115,725	91,471	$ 76,042
Funded status of the Plans at December 31	(42,741)	(39,945)
Defined Benefit Plan, Liability
Accumulated benefit obligation	113,600	94,500
Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets [Abstract]
Aggregate projected benefit obligation	119,708	131,416
Aggregate fair value of plan assets	76,313	91,471
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Aggregate accumulated benefit obligation	53,720	49,285
Aggregate fair value of plan assets	$ 18,970	$ 16,811
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate for determining net periodic pension cost (as a percent)	3.10%	3.30%	4.20%
Discount rate for determining benefit obligations at December 31 (as a percent)	3.20%	3.10%	3.30%
Rate of compensation increase for determining net periodic pension cost (as a percent)	3.80%	3.90%	4.70%
Rate of compensation increase for determining benefit obligations at December 31 (as a percent)	3.80%	3.80%	3.90%
Expected rate of return on plan assets for determining net periodic pension cost (as a percent)	4.90%	5.00%	6.20%

Pension and Severance Plans (82

Pension and Severance Plans (Defined Benefit Plans - Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan [Abstract]
Prepaid benefit cost (included in non-current assets)	$ 656	$ 0
Accrued benefit liability (included in pension and severance obligations)	(43,397)	(39,945)
Net amount recognized at year end	$ (42,741)	$ (39,945)

Pension and Severance Plans (Im

Pension and Severance Plans (Impact on Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Balance at beginning of period	$ 1,403,404	$ 1,217,536	$ 1,129,449
Total other comprehensive income (loss)	16,257	8,346	30,387
Balance at end of period	1,690,779	1,403,404	1,217,536
Prior Service Cost
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Balance at beginning of period	582	560
Amortization included in net periodic pension cost	21	22
Net gain (loss) arising during period	0	0
Total other comprehensive income (loss)	21	22
Balance at end of period	603	582	560
Estimated amortization of cost to be included in 2018 net periodic pension cost	1
Actuarial Net Gain (Loss)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Balance at beginning of period	556	(1,985)
Amortization included in net periodic pension cost	69	73
Net gain (loss) arising during period	5,075	2,468
Total other comprehensive income (loss)	5,144	2,541
Balance at end of period	5,700	556	(1,985)
Estimated amortization of cost to be included in 2018 net periodic pension cost	(147)
Total
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Balance at beginning of period	1,138	(1,425)
Amortization included in net periodic pension cost	90	95
Net gain (loss) arising during period	5,075	2,468
Total other comprehensive income (loss)	5,165	2,563
Balance at end of period	6,303	$ 1,138	$ (1,425)
Estimated amortization of cost to be included in 2018 net periodic pension cost	$ (146)

Pension and Severance Plans (Ch

Pension and Severance Plans (Changes and Components) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan [Abstract]
Service cost	$ 33,823	$ 33,854	$ 12,481
Interest cost	4,067	3,641	2,954
Expected return on plan assets	(4,537)	(3,788)	(3,330)
Amortization of prior service cost	30	35	34
Recognized actuarial (gain) loss	84	94	91
Net periodic pension cost	33,467	33,836	12,230
Curtailment loss	574	0	0
Settlement (gain) loss	383	128	27
Total pension expense	$ 34,424	$ 33,964	$ 12,257

Pension and Severance Plans (85

Pension and Severance Plans (Defined Benefit Plans - Allocation of plan assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 115,725	$ 91,471	$ 76,042
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55,873	34,145
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33,699	35,304
Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,098	10,419
Level 1 | US Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16,854	12,602
Level 1 | Foreign Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16,826	8,825
Level 1 | Foreign Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22,193	12,718
Level 1 | US Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,188	2,859
Level 1 | U.S. Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,144	1,980
Level 1 | Foreign Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,211	11,001
Level 1 | Foreign Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	520	0
Level 1 | Foreign Treasury Notes [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,686	0
Level 1 | Foreign Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,787	10,044
Level 1 | Taiwan Retirement Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10,094	8,972
Level 1 | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	584	0
Level 2 | US Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	830	0
Level 2 | U.S. Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	0
Level 2 | Foreign Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,270	7,727
Level 2 | Foreign Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,058	1,693
Level 2 | Foreign Guaranteed Investment Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14,138	2,445
Level 2 | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 239	$ 186
Japan | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	37.00%
Japan | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	60.00%
Japan | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	3.00%
Korea | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	50.00%
Korea | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	40.00%
Korea | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	10.00%
Philippines | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	56.00%
Philippines | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	40.00%
Philippines | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	4.00%

Pension and Severance Plans (86

Pension and Severance Plans (Defined Benefit Plans - Expected future contributions and other disclosures) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Defined Benefit Plan [Abstract]
Expected contributions in next fiscal year	$ 23,000
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2,018	6,288
2,019	7,516
2,020	9,538
2,021	11,602
2,022	14,143
2023 to 2027	$ 107,557

Pension and Severance Plans (87

Pension and Severance Plans (Defined Contribution Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan [Abstract]
Cost recognized	$ 10.4	$ 8.8	$ 8.6

Accumulated Other Comprehensi88

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,403,404	$ 1,217,536	$ 1,129,449
Total other comprehensive income (loss)	16,257	8,346	30,387
Balance at end of period	1,690,779	1,403,404	1,217,536
Defined Benefit Pension
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	1,138	(1,425)
Other comprehensive income (loss) before reclassifications	5,075	2,468
Amounts reclassified from accumulated other comprehensive (loss) income	90	95
Total other comprehensive income (loss)	5,165	2,563
Balance at end of period	6,303	1,138	(1,425)
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	5,124	(659)
Other comprehensive income (loss) before reclassifications	11,092	5,783
Amounts reclassified from accumulated other comprehensive (loss) income	0	0
Total other comprehensive income (loss)	11,092	5,783
Balance at end of period	16,216	5,124	(659)
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	6,262	(2,084)
Other comprehensive income (loss) before reclassifications	16,167	8,251
Amounts reclassified from accumulated other comprehensive (loss) income	90	95
Total other comprehensive income (loss)	16,257	8,346
Balance at end of period	$ 22,519	$ 6,262	$ (2,084)

Fair Value Measurements (Detail

Fair Value Measurements (Details) - Recurring - Level 1 - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair value assets measured on recurring basis
Cash equivalent money market funds (Level 1)	$ 121,627	$ 39,548
Restricted cash money market funds (Level 1)	$ 2,000	$ 2,000

Fair Value Measurements (Debt)

Fair Value Measurements (Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	$ 1,385,632	$ 1,506,558
Senior notes (Level 1) | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	745,943	954,765
Revolving credit facilities and term loans (Level 2) | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	639,689	551,793
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	1,364,429	1,474,830
Carrying Value | Senior notes (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	723,867	922,140
Carrying Value | Revolving credit facilities and term loans (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	$ 640,562	$ 552,690

Commitments and Contingencies91

Commitments and Contingencies (Details) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2015USD ($)payment	Dec. 31, 2014USD ($)	Dec. 31, 2017USD ($)
Loss Contingencies [Line Items]
Non-lease long-term supply contract, remaining amount			$ 18.3
Patent License Litigation
Loss Contingencies [Line Items]
Amount awarded to other party	$ 155		38.8
Number of quarterly settlement payments | payment	16
Litigation settlement, expense		$ 87.1
Litigation settlement interest			$ 1
Cost of Sales | Patent License Litigation
Loss Contingencies [Line Items]
Litigation settlement, expense		75.3
Interest Expense | Patent License Litigation
Loss Contingencies [Line Items]
Litigation settlement, expense		$ 11.8

Commitments and Contingencies92

Commitments and Contingencies (Future minimum lease payments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 26,439
2,019	21,740
2,020	13,694
2,021	10,530
2,022	8,468
Thereafter	28,955
Total	109,826
Rent expense	$ 48,100	$ 43,800	$ 24,500

Business Segments, Customer C93

Business Segments, Customer Concentrations and Geographic Information (Business Segments) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment									1
Net sales	$ 1,148,423	$ 1,135,027	$ 989,447	$ 913,600	$ 1,021,613	$ 1,086,014	$ 917,326	$ 868,682	$ 4,186,497	$ 3,893,635	$ 2,884,603
Property, plant and equipment, net	2,695,065				2,564,648				2,695,065	2,564,648
China
Segment Reporting Information [Line Items]
Property, plant and equipment, net	528,739				500,319				528,739	500,319
Japan
Segment Reporting Information [Line Items]
Net sales									1,208,822	1,158,318	372,810
Property, plant and equipment, net	246,223				245,233				246,223	245,233
Asia Pacific
Segment Reporting Information [Line Items]
Net sales									827,061	627,177	609,409
Europe, Middle East and Africa
Segment Reporting Information [Line Items]
Net sales									536,552	487,584	489,842
Total foreign countries
Segment Reporting Information [Line Items]
Net sales									2,572,435	2,273,079	1,472,061
Property, plant and equipment, net	2,684,548				2,552,689				2,684,548	2,552,689
United States
Segment Reporting Information [Line Items]
Net sales									1,614,062	1,620,556	$ 1,412,542
Property, plant and equipment, net	10,517				11,959				10,517	11,959
Korea
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,131,271				1,130,147				1,131,271	1,130,147
Malaysia
Segment Reporting Information [Line Items]
Property, plant and equipment, net	47,922				36,248				47,922	36,248
Philippines
Segment Reporting Information [Line Items]
Property, plant and equipment, net	309,425				313,885				309,425	313,885
Portugal
Segment Reporting Information [Line Items]
Property, plant and equipment, net	64,578				0				64,578	0
Taiwan
Segment Reporting Information [Line Items]
Property, plant and equipment, net	356,174				326,614				356,174	326,614
Other foreign countries
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 216				$ 243				$ 216	$ 243
Customer One | Sales | Customer Concentration Risk
Segment Reporting Information [Line Items]
Concentration risk (as a percent)										12.70%	14.40%
Customer Two | Sales | Customer Concentration Risk
Segment Reporting Information [Line Items]
Concentration risk (as a percent)									14.30%	15.80%	11.00%
Advanced Products
Segment Reporting Information [Line Items]
Net sales									$ 1,950,340	$ 1,679,529	$ 1,432,493
Mainstream Products
Segment Reporting Information [Line Items]
Net sales									$ 2,236,157	$ 2,214,106	$ 1,452,110

Quarterly Results (Unaudited)94

Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended								12 Months Ended
	May 31, 2017	Nov. 30, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Net sales			$ 1,148,423	$ 1,135,027	$ 989,447	$ 913,600	$ 1,021,613	$ 1,086,014	$ 917,326	$ 868,682	$ 4,186,497	$ 3,893,635	$ 2,884,603
Gross profit			225,494	216,638	172,235	142,906	227,187	213,800	131,606	122,884	757,273	695,477	479,265
Operating income			110,128	98,237	168,293	24,655	126,689	114,615	30,542	22,094	401,313	293,940	164,839
Income tax (benefit) expense			(12,782)	18,752	32,573	439	18,534	24,086	3,360	1,873	38,982	47,853	28,035
Net income (loss)			101,943	55,630	116,459	(9,144)	101,202	61,141	5,366	(405)	264,888	167,304	53,893
Net income (loss) attributable to Amkor			$ 100,770	$ 54,435	$ 115,507	$ (10,006)	$ 100,263	$ 60,089	$ 4,713	$ (875)	$ 260,706	$ 164,190	$ 51,098
Basic (in dollars per share)			$ 0.42	$ 0.23	$ 0.48	$ (0.04)	$ 0.42	$ 0.25	$ 0.02	$ 0	$ 1.09	$ 0.69	$ 0.22
Diluted (in dollars per share)			$ 0.42	$ 0.23	$ 0.48	$ (0.04)	$ 0.42	$ 0.25	$ 0.02	$ 0	$ 1.09	$ 0.69	$ 0.22
Condensed Income Statements, Captions [Line Items]
Proceeds from sale of property, plant and equipment											$ 141,530	$ 45,635	$ 6,945
Gain on sale K1 factory											2,648	(1,390)	(1,190)
Net tax benefit from U.S. tax reform											$ 41,554	$ 0	$ 0
Korea
Condensed Income Statements, Captions [Line Items]
Proceeds from sale of property, plant and equipment	$ 142,400	$ 142,400
Gain on sale K1 factory	$ 108,100	$ 108,100

Schedule II - Valuation and Q95

Schedule II - Valuation and Qualifying Accounts (Details) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 83,338	$ 165,367	$ 168,105	$ 149,847
Additions (Credited) Charged to Expense	(116,917)	7,729	18,507
Write-offs	(489)	(15,091)	(248)
Other	35,377	4,624	(1)
Balance at End of Period	$ 83,338	$ 165,367	$ 168,105