Amkor Technology (AMKR) 10-K 22 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 15, 2019	Jun. 29, 2018
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, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		239,572,534
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 872
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Net sales	$ 4,316,466	$ 4,207,031	$ 3,927,849
Cost of sales	3,605,901	3,445,952	3,217,958
Gross profit	710,565	761,079	709,891
Selling, general and administrative	295,239	297,021	284,094
Research and development	157,182	166,627	117,210
Gain on sale of real estate	0	(108,109)	0
Total operating expenses	452,421	355,539	401,304
Operating income	258,144	405,540	308,587
Interest expense	78,946	83,839	79,668
Interest expense, related party	0	1,715	4,969
Other (income) expense, net	(6,617)	12,490	(5,745)
Total other expense, net	72,329	98,044	78,892
Income before taxes	185,815	307,496	229,695
Income tax expense	56,250	39,791	51,042
Net income	129,565	267,705	178,653
Net income attributable to noncontrolling interests	(2,473)	(4,155)	(3,123)
Net income attributable to Amkor	$ 127,092	$ 263,550	$ 175,530
Net income attributable to Amkor per common share:
Basic (in dollars per share)	$ 0.53	$ 1.10	$ 0.74
Diluted (in dollars per share)	$ 0.53	$ 1.10	$ 0.74
Shares used in computing per common share amounts:
Basic (in shares)	239,329	238,937	237,416
Diluted (in shares)	239,741	239,651	238,034

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 129,565	$ 267,705	$ 178,653
Other comprehensive income (loss), net of tax:
Adjustments to unrealized components of defined benefit pension plans	(3,644)	5,165	2,563
Foreign currency translation	4,937	11,092	5,783
Total other comprehensive income (loss)	1,293	16,257	8,346
Comprehensive income	130,858	283,962	186,999
Comprehensive income attributable to noncontrolling interests	(2,473)	(4,155)	(3,123)
Comprehensive income attributable to Amkor	$ 128,385	$ 279,807	$ 183,876

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 681,569	$ 596,364
Restricted cash	2,589	2,000
Accounts receivable, net of allowances of $677 and $803, respectively	724,456	798,264
Inventories	230,589	213,649
Other current assets	32,005	33,727
Total current assets	1,671,208	1,644,004
Property, plant and equipment, net	2,650,448	2,695,065
Goodwill	25,720	25,036
Restricted cash	3,893	4,487
Other assets	144,178	139,796
Total assets	4,495,447	4,508,388
Current liabilities:
Short-term borrowings and current portion of long-term debt	114,579	123,848
Trade accounts payable	530,398	569,085
Capital expenditures payable	255,237	294,258
Accrued expenses	258,209	330,868
Total current liabilities	1,158,423	1,318,059
Long-term debt	1,217,732	1,240,581
Pension and severance obligations	184,321	182,216
Other non-current liabilities	79,071	47,823
Total liabilities	2,639,547	2,788,679
Commitments and contingencies (Note 15)
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, 285,352 and 285,129 shares issued, and 239,385 and 239,184 shares outstanding, respectively	285	285
Additional paid-in capital	1,909,425	1,903,357
Retained earnings (accumulated deficit)	113,189	(13,903)
Accumulated other comprehensive income (loss)	23,812	22,519
Treasury stock, at cost, 45,967 and 45,945 shares, respectively	(216,171)	(215,982)
Total Amkor stockholders’ equity	1,830,540	1,696,276
Noncontrolling interests in subsidiaries	25,360	23,433
Total equity	1,855,900	1,719,709
Total liabilities and equity	$ 4,495,447	$ 4,508,388

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance	$ 677	$ 803
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)	285,352	285,129
Common stock, shares outstanding (in shares)	239,385	239,184
Treasury stock, shares	45,967	45,945

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Total Amkor Stockholders' Equity	Common Stock	Additional Paid- In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Noncontrolling Interest in Subsidiaries
Balance at beginning of period, shares at Dec. 31, 2015			282,724,000
Balance at beginning of period, shares at Dec. 31, 2015							(45,719,000)
Balance at beginning 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	178,653
Net income attributable to Amkor	175,530	175,530			175,530
Net income attributable to noncontrolling interests	3,123							3,123
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 to noncontrolling interests	(548)							(548)
Balance at end of period, shares at Dec. 31, 2016			284,479,000
Balance at end of period, shares at Dec. 31, 2016							(45,814,000)
Balance at end of period at Dec. 31, 2016	1,429,517	1,409,692	$ 284	1,895,089	(277,453)	6,262	$ (214,490)	19,825
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	267,705
Net income attributable to Amkor	263,550	263,550			263,550
Net income attributable to noncontrolling interests	4,155							4,155
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 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	$ 1,719,709	1,696,276	$ 285	1,903,357	(13,903)	22,519	$ (215,982)	23,433
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	129,565
Net income attributable to Amkor	127,092	127,092			127,092
Net income attributable to noncontrolling interests	2,473							2,473
Total other comprehensive income (loss)	1,293	1,293				1,293
Treasury stock acquired through surrender of shares for tax withholding, shares							(22,000)
Treasury stock acquired through surrender of shares for tax withholding	(189)	(189)					$ (189)
Issuance of stock through share-based compensation plans, shares			223,000
Issuance of stock through share-based compensation plans	1,050	1,050		1,050
Share-based compensation	5,018	5,018		5,018
Subsidiary dividends to noncontrolling interests	$ (546)							(546)
Balance at end of period, shares at Dec. 31, 2018	285,352		285,352,000
Balance at end of period, shares at Dec. 31, 2018	(45,967)						(45,967,000)
Balance at end of period at Dec. 31, 2018	$ 1,855,900	$ 1,830,540	$ 285	$ 1,909,425	$ 113,189	$ 23,812	$ (216,171)	$ 25,360

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 129,565	$ 267,705	$ 178,653
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	571,961	581,940	555,186
Gain on sale of real estate	0	(108,109)	0
Amortization of deferred debt issuance costs and premiums	1,120	1,235	1,403
Deferred income taxes	(13,110)	(42,189)	1,443
Loss on debt retirement	1,512	4,835	0
Loss (gain) on disposal of fixed assets, net	5,310	(2,648)	1,390
Share-based compensation	5,018	5,145	3,251
Proceeds from insurance recovery for property, plant and equipment	(1,371)	0	(15,166)
Other, net	3,929	(8,143)	2,858
Changes in assets and liabilities, net of acquisitions:
Accounts receivable	80,571	(133,814)	(55,184)
Inventories	(16,310)	(36,307)	(8,623)
Other current assets	4,329	(2,473)	1,124
Other assets	1,986	(458)	1,037
Trade accounts payable	(43,490)	67,574	48,581
Accrued expenses	(78,136)	29,424	48,159
Pension and severance obligations	(4,653)	23,881	1,625
Other non-current liabilities	15,179	(29,331)	(36,335)
Net cash provided by operating activities	663,410	618,267	729,402
Cash flows from investing activities:
Payments for property, plant and equipment	(547,122)	(550,943)	(650,038)
Proceeds from sale of property, plant and equipment	2,841	141,530	45,635
Proceeds from insurance recovery for property, plant and equipment	1,371	0	15,166
Acquisition of business, net of cash acquired	0	(43,771)	0
Other investing activities	5,527	(1,648)	(190)
Net cash used in investing activities	(537,383)	(454,832)	(589,427)
Cash flows from financing activities:
Proceeds from revolving credit facilities	0	75,000	125,000
Payments of revolving credit facilities	(75,000)	0	(255,000)
Proceeds from short-term debt	23,341	77,781	49,131
Payments of short-term debt	(46,631)	(70,236)	(49,500)
Proceeds from issuance of long-term debt	596,226	223,976	46,000
Payments of long-term debt	(535,738)	(405,269)	(32,078)
Payments of long-term debt, related party	0	(17,837)	0
Payments of capital lease obligations	(3,930)	(5,340)	(2,543)
Payment of deferred consideration for purchase of facility	0	(3,890)	0
Proceeds from issuance of stock through share-based compensation plans	1,050	3,124	8,247
Other financing activities	59	(2,195)	(1,436)
Net cash used in financing activities	(40,623)	(124,886)	(112,179)
Effect of exchange rate fluctuations on cash, cash equivalents and restricted cash	(204)	8,807	351
Net increase in cash, cash equivalents and restricted cash	85,200	47,356	28,147
Cash, cash equivalents and restricted cash, beginning of period	602,851	555,495	527,348
Cash, cash equivalents and restricted cash, end of period	688,051	602,851	555,495
Cash paid during the period for:
Interest	77,575	83,808	86,777
Income taxes	63,080	61,878	32,174
Non-cash investing and financing activities:
Property, plant and equipment included in capital expenditures payable	256,070	294,912	146,080
Equipment acquired through capital lease	$ 17,163	$ 929	$ 6,358

Description of Business and Sum

Description of Business and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
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. Effective January 1, 2018, we adopted Accounting Standards Update (ASU) 2014-09, Revenue from Contracts with Customers (Topic 606) , using the full retrospective transition method as discussed in Note 2 . All amounts and disclosures set forth in this Form 10-K reflect these changes as of the applicable dates and for the applicable periods. 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. 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, 2018 , the combined book value of the assets and liabilities associated with these Philippine realty corporations included in our Consolidated Balance Sheet was $17.0 million and $0.2 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, 2018 , 2017 or 2016 . 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 16 ). 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, 2018 , 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 15 . 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 consist of raw materials and purchased components, and 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. The balance of goodwill in our Consolidated Balance Sheets reflects adjustments for foreign currency translation. 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 14 for further discussion of fair value measurements. Revenue Recognition We recognize revenue, net of sales, use, value-added and other similar taxes, as a performance obligation is satisfied in an amount reflecting the consideration to which we expect to be entitled. We apply a five-step approach in determining the amount and timing of revenue to be recognized: (1) identifying the contract with a customer; (2) identifying the performance obligations in the contract; (3) determining the transaction price; (4) allocating the transaction price to the performance obligations in the contract; and (5) recognizing revenue when the performance obligation is satisfied. Substantially all of our revenue is recognized as services are rendered. Our packaging and test services are our performance obligations to our customers. Our packaging services include wafer bump, probe and assembly. We provide packaging and test services to our customers either individually or as part of a combined offering. In a combined offering, we account for the individual services separately if they are determined to be distinct. We determine a service to be distinct if it is separately identifiable from other services in the combined offering and if a customer can benefit from the unique service on its own or with other resources that are readily available to the customer. The consideration, including variable consideration, is allocated between the distinct services in a combined offering based upon the stand-alone selling prices of the individual services. Our services involve a high degree of specialization which are unique based on the design and purpose of the customer’s wafers. Accordingly, our negotiated pricing reflects the customized nature of our services and represents a customer-specific stand-alone selling price. We recognize revenue as services are rendered, which generally occurs over the course of two to three weeks. Services are generally billed at completion of each individual packaging or test service or in some instances at the completion of all services in a combined offering. We recognize revenue over time as services are rendered because our services create or enhance the customer’s wafer. We utilize an input method (cost incurred plus estimated margin) to determine the amount of revenue to recognize for in-process, but incomplete, customer orders at a reporting date. During the period of providing our services, we generally do not control or take ownership of customers' wafers, nor do we include the cost of the wafer in our cost calculations. We believe that a cost-based input method is the most appropriate manner to measure how we satisfy our performance obligations to customers because the effort and costs incurred to package and/or test customer wafers are not linear over the duration of these services. Shipping and handling costs are accounted for as a cost to fulfill our performance obligations to customers. Accordingly, we record customer payments of shipping and handling costs as a component of net sales, and the costs incurred for shipping and handling are then charged to cost of sales. Unbilled receivables are revenues that have been recognized for performance obligations that have been satisfied, or partially satisfied, in advance of billing the customer. Revenue may be recognized in advance of billing as our contracts provide us with an unconditional right to consideration for work that is performed. Total unbilled receivables as of December 31, 2018 and 2017 were $89.3 million and $101.9 million , respectively. These amounts are included in accounts receivable, net of allowances in our Consolidated Balance Sheets. 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 (“SAB 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, which ended during the fourth quarter of 2018, 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. For the year ended December 31, 2017, we reported provisional amounts for the income tax effects of the Tax Act for which the accounting was incomplete, but a reasonable estimate could be determined. During the quarter ended December 31, 2018, we updated our provisional estimate of the impact of the Tax Act. Our accounting for the impact of the Tax Act is now complete in accordance with SAB 118. 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, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Standards	New Accounting Standards Recently Adopted Standards In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) , which was subsequently amended and clarified. The standard 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. The standard permits the use of either full retrospective or modified retrospective methods of adoption. Effective January 1, 2018, we adopted the requirements of Topic 606 using the full retrospective transition method. The new standard resulted in a change to the timing of revenue recognition, whereby revenue is recognized "over time" as services are performed rather than at a "point in time," generally upon shipment. The new standard also resulted in an increase in accounts receivables, net and a related decrease in inventories and deferred revenues. In accordance with Topic 606, we applied the following principles in connection with the adoption of the new standard: • We do not disclose the value of unsatisfied performance obligations for contracts with an original expected length of one year or less. • We do not adjust the promised amount of consideration for the effects of a significant financing component when we expect, at contract inception, that the period between when the entity transfers a promised good or service to a customer and when the customer pays for that good or service will be one year or less. • We exclude sales, use, value-added and similar taxes from the transaction price, without performing a jurisdiction-by-jurisdiction assessment. The adoption of the standard impacted our previously reported results as follows: For the Year Ended December 31, 2017 As New Accounting Pronouncement Adjustment As Adjusted (In thousands, except per share data) Income Statement: Net sales $ 4,186,497 $ 20,534 $ 4,207,031 Cost of sales 3,429,224 16,728 3,445,952 Gross Profit 757,273 3,806 761,079 Income tax expense 38,982 809 39,791 Net income 264,888 2,817 267,705 Net income attributable to Amkor 260,706 2,844 263,550 Net income attributable to Amkor per common share - diluted 1.09 0.01 1.10 For the Year Ended December 31, 2016 As Reported New Accounting Pronouncement Adjustment As Adjusted (In thousands, except per share data) Income Statement: Net sales $ 3,893,635 $ 34,214 $ 3,927,849 Cost of sales 3,198,158 19,800 3,217,958 Gross Profit 695,477 14,414 709,891 Income tax expense 47,853 3,189 51,042 Net income 167,304 11,349 178,653 Net income attributable to Amkor 164,190 11,340 175,530 Net income attributable to Amkor per common share - diluted 0.69 0.05 0.74 December 31, 2017 As New Accounting Pronouncement Adjustment As Adjusted (In thousands) Balance Sheet: Accounts receivable, net $ 692,287 $ 105,977 $ 798,264 Inventories 326,492 (112,843 ) 213,649 Other assets 146,051 (6,255 ) 139,796 Accrued expenses 374,598 (43,730 ) 330,868 Other non-current liabilities 46,144 1,679 47,823 Accumulated deficit (1) (42,851 ) 28,948 (13,903 ) (1) The adjustment to accumulated deficit includes the 2017 and 2016 net income impact for the adoption of Topic 606 of $2.8 million and $11.3 million , respectively. The adjustment also includes the cumulative impact to our 2016 beginning accumulated deficit of $14.8 million . The adoption of the standard had no impact on cash provided by or used in operating, investing, or financing activities on our consolidated cash flow statements. 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 be presented in the statement of income as nonoperating expenses. ASU 2017-07 is effective for reporting periods beginning after December 15, 2017 and applied retrospectively. We adopted ASU 2017-07 on January 1, 2018 and estimated the impact on the prior comparative period information presented in the consolidated financial statements applying the principles permitted by the standard. For the years ended December 31, 2017 and 2016, the retrospective application resulted in a $0.6 million and $0.1 million reclassification of pension costs from operating income to other (income) expense, net in the Consolidated Statements of Income for the respective periods. Refer to Note 12 for additional information. Recently Issued Standards In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) , which was subsequently amended and clarified. ASU 2016-02 requires a dual approach for lease 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 and requires either a modified retrospective transition approach with application in all comparative periods presented, or an alternative transition method, which permits a company to use its effective date as the date of initial application without restating comparative period financial statements. Early adoption is permitted. We plan to adopt this standard in the first quarter of the fiscal year ending December 31, 2019 using the alternative transition method with the effective date as of January 1, 2019. We are in the process of finalizing the impact that this new standard will have on our financial statements and disclosures. We expect the adoption will result in a significant portion of the Company's discounted present value of future minimum operating lease obligations to be included on our Consolidated Balance Sheets ( Note 15 ). We do not expect it to have a material impact on our Consolidated Statements of Income.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2018
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.

Share-Based Compensation Plans

Share-Based Compensation Plans	12 Months Ended
	Dec. 31, 2018
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, 2018 , 2017 and 2016 , we recognized share-based compensation attributable to stock options and restricted shares of $5.0 million , $5.1 million and $3.3 million , respectively, primarily in selling, general and administrative expenses. The corresponding deferred income tax benefits for stock options or restricted shares is $1.0 million and $2.4 million for 2018 and 2017 , respectively. There were no deferred income tax benefits for 2016 . Equity Incentive Plan Second Amended and Restated 2007 Equity Incentive Plan. The Second 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, 2018 there were 7.8 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, 2018 : 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, 2017 4,752 $ 8.86 Granted 474 9.40 Exercised (148) 7.10 Forfeited or expired (335) 11.40 Outstanding at December 31, 2018 4,743 $ 8.79 7.07 $ 1,443 Fully vested at December 31, 2018 and expected to vest thereafter 4,673 $ 8.77 7.05 $ 1,443 Exercisable at December 31, 2018 2,634 $ 8.06 6.05 $ 1,423 The following assumptions were used to calculate the weighted-average fair values of the options granted: For the Year Ended December 31, 2018 2017 2016 Expected life (in years) 6.0 5.7 6.5 Risk-free interest rate 2.7 % 1.9 % 1.5 % Volatility 42 % 43 % 48 % Dividend yield — — — Weighted-average grant date fair value per option granted $ 4.17 $ 4.24 $ 2.89 Total unrecognized compensation expense from stock options was $7.5 million as of December 31, 2018 , which is expected to be recognized over a weighted-average period of approximately 2.2 years beginning January 1, 2019 . 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, 2018 : Number of Shares (In thousands) Weighted- average Grant Date Fair Value (Per Share) Non-vested at December 31, 2017 188 $ 10.15 Awards granted 35 8.56 Awards vested (76 ) 10.43 Awards forfeited — — Non-vested at December 31, 2018 147 9.63 Total unrecognized compensation cost from restricted shares was $1.1 million as of December 31, 2018 , which is expected to be recognized over a weighted-average period of approximately 1.8 years beginning January 1, 2019 .

Other Income and Expense

Other Income and Expense	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 (In thousands) Interest income $ (4,133 ) $ (3,215 ) $ (1,326 ) Foreign currency (gain) loss, net 1,451 11,823 (3,592 ) Loss on debt retirement 1,512 4,835 — Other (income) expense, net (5,447 ) (953 ) (827 ) Total other (income) expense, net $ (6,617 ) $ 12,490 $ (5,745 )

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
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 periods beginning January 1, 2018. In 2017, we recognized a $41.6 million net benefit consisting of the one-time transition tax net of tax credits generated, remeasurement of deferred taxes, and the release of valuation allowance against U.S. deferred tax assets for the provisional estimate of the impact of the Tax Act. During the quarter ended December 31, 2018, we adjusted our provisional estimate of the impact of the Tax Act, primarily in connection with clarifications provided in proposed foreign tax credit regulations issued during 2018, resulting in an income tax expense in the quarter of $22.3 million . Our accounting for the impact of the Tax Act is now complete in accordance with SEC staff issued SAB No. 118. Geographic sources of income (loss) before taxes and equity in earnings of unconsolidated affiliate are as follows: For the Year Ended December 31, 2018 2017 2016 (In thousands) United States $ 5,535 $ 26,040 $ (10,880 ) Foreign 180,280 281,456 240,575 Income before taxes $ 185,815 $ 307,496 $ 229,695 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, 2018 2017 2016 (In thousands) Current: Federal $ 22,003 $ — $ — State 39 11 22 Foreign 47,318 81,969 49,577 69,360 81,980 49,599 Deferred: Federal 5,468 (34,787 ) — State 2,993 (4,072 ) — Foreign (21,571 ) (3,330 ) 1,443 (13,110 ) (42,189 ) 1,443 Income tax expense $ 56,250 $ 39,791 $ 51,042 The reconciliation between the U.S. federal statutory income tax rate of 21% for 2018 and 35% for 2017 and 2016 and our income tax expense is as follows: For the Year Ended December 31, 2018 2017 2016 (In thousands) U.S. federal statutory income tax rate $ 39,021 $ 107,623 $ 80,393 State taxes, net of federal benefit 1,677 2,624 850 Foreign income taxed at different rates 6,741 (50,243 ) (19,279 ) Foreign exchange (loss) gain (3,797 ) 29,756 (1,127 ) Change in valuation allowance (12,662 ) (6,763 ) (7,903 ) Adjustments related to prior years 267 3,329 (2,648 ) U.S. tax reform (the Tax Act) 22,284 (41,554 ) — Income tax credits generated (18,106 ) (7,296 ) (40,301 ) Repatriation of foreign earnings and profits 387 719 25,604 Expiration of net operating losses and credits 19,462 166 15,092 Other 976 1,430 361 Income tax expense $ 56,250 $ 39,791 $ 51,042 The change in valuation allowance for 2018 , 2017 and 2016 , excluding the impact of the Tax Act, is primarily the result of changes in net operating loss and tax credit carryforwards for which no tax expense or benefit has been recognized. Prior to 2018, the benefit of foreign income taxed at different rates increased as foreign income before tax has increased. The decrease in the U.S. federal statutory income tax rate to 21% in 2018 has reduced the impact of foreign income taxed at different rates than the U.S. rate. The following is a summary of the components of our deferred tax assets and liabilities: December 31, 2018 2017 (In thousands) Deferred tax assets: Net operating loss carryforwards $ 13,207 $ 53,130 Income tax credits 107,532 23,998 Property, plant and equipment 38,050 35,479 Deferred interest expense 5,415 — Accrued liabilities 68,402 68,091 Receivable 31,729 32,719 Unrealized foreign exchange loss 1,410 1,924 Other 14,545 12,682 Total deferred tax assets 280,290 228,023 Valuation allowance (118,560 ) (83,251 ) Total deferred tax assets net of valuation allowance 161,730 144,772 Deferred tax liabilities: Property, plant and equipment 14,605 15,754 Deferred gain 11,651 939 Unrealized foreign exchange gain 1,695 8,383 Unbilled receivables 9,515 8,217 Other 5,805 4,566 Total deferred tax liabilities 43,271 37,859 Net deferred tax assets $ 118,459 $ 106,913 Recognized as: Other assets 118,697 111,353 Other non-current liabilities (238 ) (4,440 ) Total $ 118,459 $ 106,913 Valuation allowance against deferred tax assets consist of the following: December 31, 2018 2017 (In thousands) Valuation allowance: U.S. $ 77,580 $ 43,719 Foreign 40,980 39,532 Total valuation allowance $ 118,560 $ 83,251 The use of our federal net operating loss carryforward to offset the one-time transition tax required by the Tax Act resulted in a reduction in deferred tax assets for net operating loss carryforwards and created deferred tax assets for foreign income tax credit carryforwards. The increase in our valuation allowance includes the estimate of the portion of our foreign tax credit carryforwards generated in connection with the one-time transition tax included in the Tax Act projected to expire unused. 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 $1.9 million , $6.2 million and $5.6 million in tax benefits as a result of the tax holidays in 2018 , 2017 and 2016 , respectively. The benefit of the tax holidays on diluted earnings per share was approximately $0.01 , $0.03 and $0.02 for 2018 , 2017 and 2016 , respectively. Our net operating loss carryforwards (“NOLs”) are as follows: December 31, 2018 2017 Expiration (In thousands) U.S. Federal NOLs $ 25,272 $ 220,445 2021-2024 U.S. State NOLs 108,011 121,095 2019-2036 Foreign NOLs 10,686 2,967 2019-2028 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 foreign net operating loss carryforwards, we consider it more likely than not that we will not have sufficient taxable income to allow us to realize these deferred tax assets. At December 31, 2017, a portion of our U.S. federal net operating loss carryforward was reserved with a valuation allowance due to an estimate of the net operating loss carryforward not expected to be realized. At December 31, 2018, a portion of our remaining U.S. federal net operating loss carryforward was reserved with a valuation allowance due to ownership change limitations from a prior year acquisition as well as certain state net operating loss carryforwards expected to expire unused. Our tax credit carryforwards are as follows: December 31, 2018 2017 Expiration (In thousands) U.S. Foreign Tax Credits $ 84,056 $ 12,637 2026-2027 U.S. Other Tax Credits 1,117 7,104 2026-2038 Foreign Tax Credits 22,359 4,257 2019-2028 At December 31, 2018 , a portion of our U.S. foreign tax credit carryforward was reserved with a valuation allowance for the amount expected to expire unused. 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 . The income tax expense from the deemed repatriation was offset by net operating loss carryforwards and income tax credits resulting in a transition tax payable of $21.8 million . Under an election of the Tax Act, the remaining transition tax is payable over eight years beginning with tax year 2017, with 8% due in each of the first five years, 15% in year six, 20% in year seven, and 25% in year eight. 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 $91.8 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 2012-2018 . 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, and 2014-2016 Singapore tax returns. A reconciliation of the beginning and ending gross amount of unrecognized tax benefits is as follows: For the Year Ended December 31, 2018 2017 2016 (In thousands) Balance at January 1 $ 27,211 $ 23,149 $ 23,332 Additions based on tax positions related to the current year 401 1,419 1,822 Additions for tax positions of prior years 636 2,661 689 Reductions for tax positions of prior years (2,958 ) (1 ) (2,589 ) Reductions from lapse of statutes of limitations (22 ) (17 ) (105 ) Balance at December 31 $ 25,268 $ 27,211 $ 23,149 The net decrease in our unrecognized tax benefits was $1.9 million from December 31, 2017 to December 31, 2018 . The decrease was primarily related to the closure of an audit. At December 31, 2018 , all of our gross unrecognized tax benefits would reduce our effective tax rate, if recognized. It is reasonably possible that unrecognized tax benefits related to entity classification and withholding taxes will decrease by up to $2.9 million due to the lapse of statutes of limitations in foreign jurisdictions. The liability related to our unrecognized tax benefits is $25.3 million as of December 31, 2018 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 $5.3 million as of December 31, 2018 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, 2018
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, 2018 2017 2016 (In thousands, except per share data) Net income available to Amkor common stockholders $ 127,092 $ 263,550 $ 175,530 Weighted-average shares outstanding — basic 239,329 238,937 237,416 Effect of dilutive securities: Stock options and restricted share awards 412 714 618 Weighted-average shares outstanding — diluted 239,741 239,651 238,034 Net income attributable to Amkor per common share: Basic $ 0.53 $ 1.10 $ 0.74 Diluted 0.53 1.10 0.74 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, 2018 2017 2016 (In thousands) Stock options and restricted share awards 3,662 3,445 1,135

Factoring of Accounts Receivabl

Factoring of Accounts Receivable	12 Months Ended
	Dec. 31, 2018
Factoring of Accounts Receivable [Abstract]
Factoring of Accounts Receivable	Factoring of Accounts Receivable For certain accounts receivable, 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, 2018 and 2017 , we sold accounts receivable totaling $873.9 million and $611.2 million , net of discounts and fees of $7.0 million and $4.6 million , respectively.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment consist of the following: December 31, 2018 2017 (In thousands) Land $ 222,884 $ 224,894 Land use rights 26,845 26,845 Buildings and improvements 1,523,065 1,384,846 Machinery and equipment 5,196,930 4,926,432 Capital lease machinery and equipment 25,874 11,859 Software and computer equipment 213,440 200,500 Furniture, fixtures and other equipment 17,204 15,722 Construction in progress 44,381 104,910 Total property, plant and equipment 7,270,623 6,896,008 Less accumulated depreciation and amortization (4,620,175 ) (4,200,943 ) Total property, plant and equipment, net $ 2,650,448 $ 2,695,065 The following table summarizes our depreciation expense: For the Year Ended December 31, 2018 2017 2016 (In thousands) Depreciation expense $ 570,304 $ 580,172 $ 552,989 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 .

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses consist of the following: December 31, 2018 2017 (In thousands) Payroll and benefits $ 124,943 $ 134,785 Income taxes payable 38,567 56,664 Deferred revenue and customer advances 16,736 14,740 Accrued severance plan obligations (Note 12) 13,179 15,190 Accrued interest 10,302 11,873 Accrued settlement costs — 37,783 Other accrued expenses 54,482 59,833 Total accrued expenses $ 258,209 $ 330,868

Debt

Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt Short-term borrowings and long-term debt consist of the following: December 31, 2018 2017 (In thousands) Debt of Amkor Technology, Inc.: Senior notes: 6.625% Senior notes, due June 2021 (1) $ — $ 200,000 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 September 2018 (2) — 75,000 $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019 (3) — — Term loan, LIBOR plus 2.70%, due December 2019 — 55,000 Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 (2) — 150,000 Term loan, fixed rate at 3.70%, due May 2020 120,000 120,000 Term loan, fund floating rate plus 1.60%, due June 2020 (4) 125,000 86,000 Term loan, LIBOR plus 2.56%, due December 2023 (2) 200,000 — Term loan, applicable bank rate plus 1.98%, due December 2028 (4) 24,000 — J-Devices Corporation: Short-term term loans, variable rate (5) 8,232 30,455 Term loans, fixed rate at 0.53%, due April 2018 — 6,744 Term loan, fixed rate at 0.86%, due June 2022 31,908 39,933 Term loan, fixed rate at 0.60%, due July 2022 6,838 8,430 Term loan, fixed rate at 1.30%, due July 2023 (1) 225,180 — Other: $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore) (6) — — Revolving credit facility, TAIFX plus the applicable bank rate, due November 2020 (Taiwan) (7) 20,000 20,000 Term loan, LIBOR plus 1.80%, due December 2019 (China) 48,000 49,000 1,334,129 1,365,533 Less: Unamortized premium and deferred debt costs, net (1,818 ) (1,104 ) Less: Short-term borrowings and current portion of long-term debt (114,579 ) (123,848 ) Long-term debt $ 1,217,732 $ 1,240,581 (1) In August 2018, we redeemed all $200 million of our 6.625% Senior Notes due 2021 ("Notes"). In accordance with the terms of the indenture governing the Notes, the redemption price was 100% of the principal amount of the Notes, plus accrued and unpaid interest. We recorded a $0.8 million charge for the write-off of the associated unamortized debt issuance costs. The redemption of the Notes was funded with proceeds from our ¥26.0 billion ( $233.2 million ) term loan agreement entered into in July 2018 by J-Devices Corporation and guaranteed by Amkor Technology, Inc. Principal is payable in quarterly installments. (2) In June 2018, we extended our $75.0 million credit facility from June 2018 to September 2018 and in September 2018, we replaced it with a $75.0 million term loan due September 2021 at LIBOR plus 2.34% . In December 2018, we entered into a $200.0 million term loan agreement to repay this $75.0 million term loan. The remaining proceeds along with cash on hand were used to repay the $141 million outstanding term loan due May 2020. Principal of the new term loan is payable at maturity date of December 2023. (3) In October 2018, we entered into a revolving credit facility agreement with availability of $30.0 million . Principal will be payable at the maturity date of October 2019. As of December 31, 2018 , $30.0 million was available to be drawn. (4) 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 in June 2020. Interest is payable quarterly in arrears. In the second quarter of 2018, we borrowed the remaining $64.0 million available under the term loan due June 2020 and repaid $55 million of the term loan due December 2019 and $9 million of the term loan due May 2020. In December 2018, we entered into a term loan agreement pursuant to which we may borrow up to $90.0 million for capital expenditures. We borrowed $24.0 million of this new term loan and used the proceeds along with $1.0 million cash on hand to repay part of the term loan due June 2020. Principal of the new term loan is payable in semiannual installments beginning June 2022 and ending at maturity date of December 2028. As of December 31, 2018 , $66.0 million was available to be drawn. In February 2019, we borrowed an additional $30.0 million of this new term loan and used the proceeds to repay $29.0 million of the term loan due June 2020. (5) We entered into various short-term loans which mature semiannually. Principal is payable in monthly installments. As of December 31, 2018 , $4.6 million was available to be drawn. (6) In July 2018, the senior secured revolving credit facility of Amkor Technology, Inc. was terminated and replaced by a new facility entered into by our subsidiary, Amkor Technology Singapore Holding Pte, Ltd., and guaranteed by Amkor Technology, Inc. We recorded a $0.4 million charge for the write-off of the associated unamortized debt issuance costs relating to the terminated credit facility. The availability for the new revolving credit facility is based on the amount of eligible accounts receivable. As of December 31, 2018 , we had availability of $250.0 million under the new senior secured revolving credit facility with no outstanding standby letters of credit. (7) In November 2015, we entered into a $39.0 million revolving credit facility. Principal is payable at maturity. As of December 31, 2018 , $19.0 million was available to be drawn. Certain of our foreign debt is collateralized by the land, buildings, equipment and accounts receivable 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, 2018 2017 Amkor Technology Korea, Inc.: $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due September 2018 — 4.01 % $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019 — — Term loan, LIBOR plus 2.70%, due December 2019 — 4.02 % Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 — 4.06 % Term Loan, fund floating rate plus 1.60%, due June 2020 4.49 % 3.29 % Term loan, LIBOR plus 2.56%, due December 2023 5.38 % — Term loan, applicable bank rate plus 1.98%, due December 2028 4.64 % — J-Devices Corporation: Short-term term loans, variable rate 0.24 % 0.22 % Amkor Technology Singapore Holdings Pte, Ltd.: $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 — — Amkor Technology Taiwan Ltd.: Revolving credit facility, TAIFX plus the applicable bank rate, due November 2020 4.26 % 3.18 % Amkor Assembly & Test (Shanghai) Co., Ltd.: Term loan, LIBOR plus 1.80%, due December 2019 4.22 % 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. From time to time, Amkor Technology, Inc. also guarantees certain debt of our subsidiaries. The agreements governing our indebtedness contain affirmative, negative and financial 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 debt covenants at December 31, 2018 and 2017 . Maturities Total Debt (In thousands) Payments due for the year ending December 31, 2019 $ 114,579 2020 323,346 2021 58,346 2022 581,723 2023 238,985 Thereafter 17,150 Total debt $ 1,334,129

Pension and Severance Plans

Pension and Severance Plans	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 (In thousands) Balance at January 1 $ 153,920 $ 136,396 $ 143,151 Provision of severance benefits 1,939 11,714 6,746 Severance payments (7,611 ) (11,787 ) (9,429 ) Foreign currency (gain) loss (5,950 ) 17,597 (4,072 ) Balance at December 31 142,298 153,920 136,396 Payments remaining with the National Pension Fund (172 ) (185 ) (182 ) Total accrued severance plan obligations at December 31 142,126 153,735 136,214 Less current portion of accrued severance plan obligations (Note 10) 13,179 15,190 14,053 Non-current portion of accrued severance plan obligations $ 128,947 $ 138,545 $ 122,161 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, 2018 and 2017 : For the Year Ended December 31, 2018 2017 (In thousands) Change in projected benefit obligation: Projected benefit obligation at January 1 $ 158,466 $ 131,416 Service cost 32,913 33,823 Interest cost 4,867 4,067 Benefits paid (6,137 ) (15,183 ) Actuarial (gain) loss (5,991 ) (1,387 ) Effects of curtailment — 573 Settlement (5,055 ) (2,496 ) Foreign exchange (gain) loss (3,351 ) 7,653 Projected benefit obligation at December 31 175,712 158,466 Change in plan assets: Fair value of plan assets at January 1 115,725 91,471 Actual gain (loss) on plan assets (4,210 ) 8,559 Employer contributions 26,899 28,073 Settlement (5,055 ) (2,496 ) Benefits paid (6,137 ) (15,183 ) Foreign exchange gain (loss) (3,852 ) 5,301 Fair value of plan assets at December 31 123,370 115,725 Funded status of the Plans at December 31 $ (52,342 ) $ (42,741 ) December 31, 2018 2017 (In thousands) Amounts recognized in the Consolidated Balance Sheets consist of: Prepaid benefit cost (included in non-current assets) $ 2,740 $ 656 Accrued benefit liability (included in pension and severance obligations) (55,082 ) (43,397 ) Net amount recognized at year end $ (52,342 ) $ (42,741 ) The accumulated benefit obligation as of December 31, 2018 and 2017 was $132.9 million and $113.6 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, 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 Amortization and settlement gain included in net periodic pension cost (1 ) (1,735 ) (1,736 ) Net gain (loss) arising during period — (1,908 ) (1,908 ) Adjustments to unrealized components of defined benefit pension plan included in other comprehensive income (loss) (1 ) (3,643 ) (3,644 ) Balance at December 31, 2018 $ 602 $ 2,057 $ 2,659 Estimated amortization of cost to be included in 2019 net periodic pension cost $ — $ (374 ) $ (374 ) Information for pension plans with benefit obligations in excess of plan assets is as follows: December 31, 2018 2017 (In thousands) Plans with underfunded or non-funded projected benefit obligation: Aggregate projected benefit obligation $ 135,967 $ 119,708 Aggregate fair value of plan assets 80,885 76,313 Plans with underfunded or non-funded accumulated benefit obligation: Aggregate accumulated benefit obligation 63,274 53,720 Aggregate fair value of plan assets 20,094 18,970 The following table summarizes total pension expense: For the Year Ended December 31, 2018 2017 2016 (In thousands) Components of net periodic pension cost and total pension expense: Service cost $ 32,913 $ 33,823 $ 33,854 Interest cost 4,867 4,067 3,641 Expected return on plan assets (5,640 ) (4,537 ) (3,788 ) Amortization of prior service cost 6 30 35 Recognized actuarial (gain) loss (147 ) 84 94 Net periodic pension cost 31,999 33,467 33,836 Curtailment loss — 574 — Settlement (gain) loss (1,639 ) 383 128 Total pension expense $ 30,360 $ 34,424 $ 33,964 The components of net periodic pension cost other than the service cost component are included in other (income) expense, net in our Consolidated Statements of Income. 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, 2018 2017 2016 Discount rate for determining net periodic pension cost 3.2 % 3.1 % 3.3 % Discount rate for determining benefit obligations at December 31 3.1 % 3.2 % 3.1 % Rate of compensation increase for determining net periodic 3.8 % 3.8 % 3.9 % Rate of compensation increase for determining benefit obligations 3.6 % 3.8 % 3.8 % Expected rate of return on plan assets for determining net periodic 4.9 % 4.9 % 5.0 % 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 33 % 63 % 4 % The fair value of our pension plan assets, by asset category utilizing the fair value hierarchy as discussed in Note 14 , is as follows: December 31, 2018 2017 (In thousands) Cash and cash equivalents (Level 1) $ 6,640 $ 1,098 Equity securities U.S. securities (Level 1) 15,069 16,854 Foreign securities (Level 1) 10,162 16,826 Foreign mutual funds (Level 1) 25,236 22,193 50,467 55,873 Debt securities U.S. government bonds (Level 1) — 2,188 U.S. government bonds (Level 2) 1,039 830 U.S. corporate bonds (Level 1) — 2,144 U.S. corporate bonds (Level 2) 29 5 Foreign government bonds (Level 1) 4,427 5,211 Foreign government bonds (Level 2) 9,545 6,270 Foreign corporate bonds (Level 1) 5,713 520 Foreign corporate bonds (Level 2) 1,951 3,058 Foreign treasury notes (Level 1) 2,587 4,686 Foreign mutual funds (Level 1) 11,188 8,787 36,479 33,699 Foreign guaranteed investment contracts (Level 2) 18,120 14,138 Taiwan retirement fund (Level 1) 10,451 10,094 Other (Level 1) 680 584 Other (Level 2) 533 239 Total fair value of pension plan assets $ 123,370 $ 115,725 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 2019 . 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) 2019 $ 7,922 2020 10,369 2021 12,229 2022 14,979 2023 16,341 2024 to 2028 129,703 Defined Contribution Plans We sponsor defined contribution plans in Korea, Malaysia, Taiwan and the U.S. Total defined contribution expense was $12.2 million , $10.4 million and $8.8 million for 2018 , 2017 and 2016 , respectively.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2018
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, 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 Other comprehensive income (loss) before reclassifications (1,908 ) 4,937 3,029 Amounts reclassified from accumulated other comprehensive income (loss) (1,736 ) — (1,736 ) Other comprehensive income (loss) (3,644 ) 4,937 1,293 Balance at December 31, 2018 $ 2,659 $ 21,153 $ 23,812 Amounts reclassified out of accumulated other comprehensive income (loss) are included as a component of net periodic pension cost ( Note 12 ) or other (income) expense, net.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 (In thousands) Cash equivalent money market funds (Level 1) $ 74,407 $ 121,627 Restricted cash money market funds (Level 1) 2,589 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, 2018 December 31, 2017 Fair Value Carrying Value Fair Value Carrying Value (In thousands) Senior notes (Level 1) $ 526,131 $ 524,978 $ 745,943 $ 723,867 Revolving credit facilities and term loans (Level 2) 803,867 807,333 639,689 640,562 Total financial instruments $ 1,329,998 $ 1,332,311 $ 1,385,632 $ 1,364,429 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, 2018
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. At December 31, 2018 , we have no remaining liability under this settlement agreement. Leases Future minimum lease payments under noncancelable leases are as follows: For the Year Ended December 31 Operating Leases Capital Leases (In thousands) 2019 $ 32,461 $ 6,430 2020 24,630 4,555 2021 17,676 4,748 2022 10,942 936 2023 9,008 936 Thereafter 26,070 3,807 Total future minimum lease payments $ 120,787 $ 21,412 Rent expense was $43.6 million , $48.1 million and $43.8 million for 2018 , 2017 and 2016 , 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 2019 through 2025 are $10.4 million .

Business Segments, Customer Con

Business Segments, Customer Concentrations and Geographic Information	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 (In thousands) Advanced Products $ 2,118,571 $ 1,966,483 $ 1,703,052 Mainstream Products 2,197,895 2,240,548 2,224,797 Total net sales $ 4,316,466 $ 4,207,031 $ 3,927,849 (1) Advanced products include flip chip and wafer-level processing and related test services. (2) Mainstream products include wirebond packaging and related test services. Net sales by end market consist of the following : For the Year Ended December 31, 2018 2017 2016 Communications (smartphones, tablets, handheld devices) 44 % 43 % 42 % Automotive, industrial and other (driver assist, infotainment, safety, performance) 26 % 26 % 26 % Computing (datacenter, infrastructure, PC/laptop, storage) 18 % 18 % 18 % Consumer (set-top boxes, televisions, connected home, personal electronics, visual imaging) 12 % 13 % 14 % Total net sales 100 % 100 % 100 % Net sales by region based on customer headquarters location consist of the following: For the Year Ended December 31, 2018 2017 2016 (In thousands) Japan $ 1,156,797 $ 1,210,296 $ 1,162,729 Europe, Middle East and Africa 605,932 540,126 490,738 Asia Pacific (excluding Japan) 535,894 837,014 630,837 Total foreign countries 2,298,623 2,587,436 2,284,304 United States 2,017,843 1,619,595 1,643,545 Total net sales $ 4,316,466 $ 4,207,031 $ 3,927,849 One customer accounted for 10.2% , 14.3% , and 15.7% of net sales in 2018 , 2017 and 2016 , respectively. A second customer accounted for 12.9% of net sales in 2016 . Property, plant and equipment, net, based on physical location, consist of the following: December 31, 2018 2017 (In thousands) China $ 472,858 $ 528,739 Japan 219,373 246,223 Korea 1,213,838 1,131,271 Malaysia 47,491 47,922 Philippines 270,562 309,425 Portugal 63,323 64,578 Taiwan 352,576 356,174 Other foreign countries 170 216 Total foreign countries 2,640,191 2,684,548 United States 10,257 10,517 Total property, plant and equipment, net $ 2,650,448 $ 2,695,065

Quarterly Results (Unaudited)

Quarterly Results (Unaudited)	12 Months Ended
	Dec. 31, 2018
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, 2018 . 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, 2018 (c) Sep 30, 2018 Jun 30, 2018 Mar 31, 2018 Dec 31, 2017 (c) Sep 30, 2017 Jun 30, 2017 (a) Mar 31, 2017 (In thousands, except per share data) Net sales $ 1,081,271 $ 1,144,192 $ 1,065,684 $ 1,025,319 $ 1,150,478 $ 1,148,884 $ 1,008,385 $ 899,284 Gross profit 182,370 200,707 169,717 157,771 224,341 223,888 176,616 136,234 Operating income (b) 75,381 92,703 53,941 36,119 109,018 105,479 172,659 18,384 Income tax (benefit) expense 28,812 14,326 10,631 2,481 (13,613 ) 21,263 33,466 (1,325 ) Net income (loss) 28,894 57,292 33,184 10,195 101,185 60,458 120,030 (13,968 ) Net income (loss) attributable to Amkor 28,295 56,662 32,591 9,544 100,059 59,264 119,013 (14,786 ) Net income (loss) attributable to Amkor per common share: Basic $ 0.12 $ 0.24 $ 0.14 $ 0.04 $ 0.42 $ 0.25 $ 0.50 $ (0.06 ) Diluted $ 0.12 $ 0.24 $ 0.14 $ 0.04 $ 0.42 $ 0.25 $ 0.50 $ (0.06 ) (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. In the fourth quarter of 2018, we recorded a $22.3 million income tax expense to complete the accounting for the impact of the Tax Act, reducing our estimated net tax benefit of $41.6 million from 2017.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-09, 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 at December 31, 2016 $ 168,762 7,189 (15,091 ) 4,624 $ 165,484 Year ended at December 31, 2017 $ 165,484 (117,121 ) (489 ) 35,377 $ 83,251 Year ended at December 31, 2018 $ 83,251 54,421 (19,112 ) — $ 118,560 (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 S_2

Description of Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	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. Effective January 1, 2018, we adopted Accounting Standards Update (ASU) 2014-09, Revenue from Contracts with Customers (Topic 606) , using the full retrospective transition method as discussed in Note 2 . All amounts and disclosures set forth in this Form 10-K reflect these changes as of the applicable dates and for the applicable periods. 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, 2018 , the combined book value of the assets and liabilities associated with these Philippine realty corporations included in our Consolidated Balance Sheet was $17.0 million and $0.2 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, 2018 , 2017 or 2016 . 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 16 ). 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, 2018 , 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 15 . 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 consist of raw materials and purchased components, and 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. The balance of goodwill in our Consolidated Balance Sheets reflects adjustments for foreign currency translation.
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 14 for further discussion of fair value measurements.
Revenue Recognition	Revenue Recognition We recognize revenue, net of sales, use, value-added and other similar taxes, as a performance obligation is satisfied in an amount reflecting the consideration to which we expect to be entitled. We apply a five-step approach in determining the amount and timing of revenue to be recognized: (1) identifying the contract with a customer; (2) identifying the performance obligations in the contract; (3) determining the transaction price; (4) allocating the transaction price to the performance obligations in the contract; and (5) recognizing revenue when the performance obligation is satisfied. Substantially all of our revenue is recognized as services are rendered. Our packaging and test services are our performance obligations to our customers. Our packaging services include wafer bump, probe and assembly. We provide packaging and test services to our customers either individually or as part of a combined offering. In a combined offering, we account for the individual services separately if they are determined to be distinct. We determine a service to be distinct if it is separately identifiable from other services in the combined offering and if a customer can benefit from the unique service on its own or with other resources that are readily available to the customer. The consideration, including variable consideration, is allocated between the distinct services in a combined offering based upon the stand-alone selling prices of the individual services. Our services involve a high degree of specialization which are unique based on the design and purpose of the customer’s wafers. Accordingly, our negotiated pricing reflects the customized nature of our services and represents a customer-specific stand-alone selling price. We recognize revenue as services are rendered, which generally occurs over the course of two to three weeks. Services are generally billed at completion of each individual packaging or test service or in some instances at the completion of all services in a combined offering. We recognize revenue over time as services are rendered because our services create or enhance the customer’s wafer. We utilize an input method (cost incurred plus estimated margin) to determine the amount of revenue to recognize for in-process, but incomplete, customer orders at a reporting date. During the period of providing our services, we generally do not control or take ownership of customers' wafers, nor do we include the cost of the wafer in our cost calculations. We believe that a cost-based input method is the most appropriate manner to measure how we satisfy our performance obligations to customers because the effort and costs incurred to package and/or test customer wafers are not linear over the duration of these services. Shipping and handling costs are accounted for as a cost to fulfill our performance obligations to customers. Accordingly, we record customer payments of shipping and handling costs as a component of net sales, and the costs incurred for shipping and handling are then charged to cost of sales. Unbilled receivables are revenues that have been recognized for performance obligations that have been satisfied, or partially satisfied, in advance of billing the customer. Revenue may be recognized in advance of billing as our contracts provide us with an unconditional right to consideration for work that is performed. Total unbilled receivables as of December 31, 2018 and 2017 were $89.3 million and $101.9 million , respectively. These amounts are included in accounts receivable, net of allowances in our Consolidated Balance Sheets.
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 (“SAB 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, which ended during the fourth quarter of 2018, 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. For the year ended December 31, 2017, we reported provisional amounts for the income tax effects of the Tax Act for which the accounting was incomplete, but a reasonable estimate could be determined. During the quarter ended December 31, 2018, we updated our provisional estimate of the impact of the Tax Act. Our accounting for the impact of the Tax Act is now complete in accordance with SAB 118. 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.

Description of Business and S_3

Description of Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	The adoption of the standard impacted our previously reported results as follows: For the Year Ended December 31, 2017 As New Accounting Pronouncement Adjustment As Adjusted (In thousands, except per share data) Income Statement: Net sales $ 4,186,497 $ 20,534 $ 4,207,031 Cost of sales 3,429,224 16,728 3,445,952 Gross Profit 757,273 3,806 761,079 Income tax expense 38,982 809 39,791 Net income 264,888 2,817 267,705 Net income attributable to Amkor 260,706 2,844 263,550 Net income attributable to Amkor per common share - diluted 1.09 0.01 1.10 For the Year Ended December 31, 2016 As Reported New Accounting Pronouncement Adjustment As Adjusted (In thousands, except per share data) Income Statement: Net sales $ 3,893,635 $ 34,214 $ 3,927,849 Cost of sales 3,198,158 19,800 3,217,958 Gross Profit 695,477 14,414 709,891 Income tax expense 47,853 3,189 51,042 Net income 167,304 11,349 178,653 Net income attributable to Amkor 164,190 11,340 175,530 Net income attributable to Amkor per common share - diluted 0.69 0.05 0.74 December 31, 2017 As New Accounting Pronouncement Adjustment As Adjusted (In thousands) Balance Sheet: Accounts receivable, net $ 692,287 $ 105,977 $ 798,264 Inventories 326,492 (112,843 ) 213,649 Other assets 146,051 (6,255 ) 139,796 Accrued expenses 374,598 (43,730 ) 330,868 Other non-current liabilities 46,144 1,679 47,823 Accumulated deficit (1) (42,851 ) 28,948 (13,903 ) (1) The adjustment to accumulated deficit includes the 2017 and 2016 net income impact for the adoption of Topic 606 of $2.8 million and $11.3 million , respectively. The adjustment also includes the cumulative impact to our 2016 beginning accumulated deficit of $14.8 million .

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 : 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, 2017 4,752 $ 8.86 Granted 474 9.40 Exercised (148) 7.10 Forfeited or expired (335) 11.40 Outstanding at December 31, 2018 4,743 $ 8.79 7.07 $ 1,443 Fully vested at December 31, 2018 and expected to vest thereafter 4,673 $ 8.77 7.05 $ 1,443 Exercisable at December 31, 2018 2,634 $ 8.06 6.05 $ 1,423
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, 2018 2017 2016 Expected life (in years) 6.0 5.7 6.5 Risk-free interest rate 2.7 % 1.9 % 1.5 % Volatility 42 % 43 % 48 % Dividend yield — — — Weighted-average grant date fair value per option granted $ 4.17 $ 4.24 $ 2.89
Restricted share activity	The following table summarizes our restricted share activity for the year ended December 31, 2018 : Number of Shares (In thousands) Weighted- average Grant Date Fair Value (Per Share) Non-vested at December 31, 2017 188 $ 10.15 Awards granted 35 8.56 Awards vested (76 ) 10.43 Awards forfeited — — Non-vested at December 31, 2018 147 9.63

Other Income and Expense (Table

Other Income and Expense (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 (In thousands) Interest income $ (4,133 ) $ (3,215 ) $ (1,326 ) Foreign currency (gain) loss, net 1,451 11,823 (3,592 ) Loss on debt retirement 1,512 4,835 — Other (income) expense, net (5,447 ) (953 ) (827 ) Total other (income) expense, net $ (6,617 ) $ 12,490 $ (5,745 )

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 (In thousands) United States $ 5,535 $ 26,040 $ (10,880 ) Foreign 180,280 281,456 240,575 Income before taxes $ 185,815 $ 307,496 $ 229,695
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, 2018 2017 2016 (In thousands) Current: Federal $ 22,003 $ — $ — State 39 11 22 Foreign 47,318 81,969 49,577 69,360 81,980 49,599 Deferred: Federal 5,468 (34,787 ) — State 2,993 (4,072 ) — Foreign (21,571 ) (3,330 ) 1,443 (13,110 ) (42,189 ) 1,443 Income tax expense $ 56,250 $ 39,791 $ 51,042
Schedule of Effective Income Tax Rate Reconciliation	The reconciliation between the U.S. federal statutory income tax rate of 21% for 2018 and 35% for 2017 and 2016 and our income tax expense is as follows: For the Year Ended December 31, 2018 2017 2016 (In thousands) U.S. federal statutory income tax rate $ 39,021 $ 107,623 $ 80,393 State taxes, net of federal benefit 1,677 2,624 850 Foreign income taxed at different rates 6,741 (50,243 ) (19,279 ) Foreign exchange (loss) gain (3,797 ) 29,756 (1,127 ) Change in valuation allowance (12,662 ) (6,763 ) (7,903 ) Adjustments related to prior years 267 3,329 (2,648 ) U.S. tax reform (the Tax Act) 22,284 (41,554 ) — Income tax credits generated (18,106 ) (7,296 ) (40,301 ) Repatriation of foreign earnings and profits 387 719 25,604 Expiration of net operating losses and credits 19,462 166 15,092 Other 976 1,430 361 Income tax expense $ 56,250 $ 39,791 $ 51,042
Schedule of Deferred Tax Assets and Liabilities	The following is a summary of the components of our deferred tax assets and liabilities: December 31, 2018 2017 (In thousands) Deferred tax assets: Net operating loss carryforwards $ 13,207 $ 53,130 Income tax credits 107,532 23,998 Property, plant and equipment 38,050 35,479 Deferred interest expense 5,415 — Accrued liabilities 68,402 68,091 Receivable 31,729 32,719 Unrealized foreign exchange loss 1,410 1,924 Other 14,545 12,682 Total deferred tax assets 280,290 228,023 Valuation allowance (118,560 ) (83,251 ) Total deferred tax assets net of valuation allowance 161,730 144,772 Deferred tax liabilities: Property, plant and equipment 14,605 15,754 Deferred gain 11,651 939 Unrealized foreign exchange gain 1,695 8,383 Unbilled receivables 9,515 8,217 Other 5,805 4,566 Total deferred tax liabilities 43,271 37,859 Net deferred tax assets $ 118,459 $ 106,913 Recognized as: Other assets 118,697 111,353 Other non-current liabilities (238 ) (4,440 ) Total $ 118,459 $ 106,913
Summary of Valuation Allowance	Valuation allowance against deferred tax assets consist of the following: December 31, 2018 2017 (In thousands) Valuation allowance: U.S. $ 77,580 $ 43,719 Foreign 40,980 39,532 Total valuation allowance $ 118,560 $ 83,251
Summary of Operating Loss Carryforwards	Our net operating loss carryforwards (“NOLs”) are as follows: December 31, 2018 2017 Expiration (In thousands) U.S. Federal NOLs $ 25,272 $ 220,445 2021-2024 U.S. State NOLs 108,011 121,095 2019-2036 Foreign NOLs 10,686 2,967 2019-2028
Summary of Tax Credit Carryforwards	Our tax credit carryforwards are as follows: December 31, 2018 2017 Expiration (In thousands) U.S. Foreign Tax Credits $ 84,056 $ 12,637 2026-2027 U.S. Other Tax Credits 1,117 7,104 2026-2038 Foreign Tax Credits 22,359 4,257 2019-2028
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, 2018 2017 2016 (In thousands) Balance at January 1 $ 27,211 $ 23,149 $ 23,332 Additions based on tax positions related to the current year 401 1,419 1,822 Additions for tax positions of prior years 636 2,661 689 Reductions for tax positions of prior years (2,958 ) (1 ) (2,589 ) Reductions from lapse of statutes of limitations (22 ) (17 ) (105 ) Balance at December 31 $ 25,268 $ 27,211 $ 23,149

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 (In thousands, except per share data) Net income available to Amkor common stockholders $ 127,092 $ 263,550 $ 175,530 Weighted-average shares outstanding — basic 239,329 238,937 237,416 Effect of dilutive securities: Stock options and restricted share awards 412 714 618 Weighted-average shares outstanding — diluted 239,741 239,651 238,034 Net income attributable to Amkor per common share: Basic $ 0.53 $ 1.10 $ 0.74 Diluted 0.53 1.10 0.74
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, 2018 2017 2016 (In thousands) Stock options and restricted share awards 3,662 3,445 1,135

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Summary of Property, plant and equipment	Property, plant and equipment consist of the following: December 31, 2018 2017 (In thousands) Land $ 222,884 $ 224,894 Land use rights 26,845 26,845 Buildings and improvements 1,523,065 1,384,846 Machinery and equipment 5,196,930 4,926,432 Capital lease machinery and equipment 25,874 11,859 Software and computer equipment 213,440 200,500 Furniture, fixtures and other equipment 17,204 15,722 Construction in progress 44,381 104,910 Total property, plant and equipment 7,270,623 6,896,008 Less accumulated depreciation and amortization (4,620,175 ) (4,200,943 ) Total property, plant and equipment, net $ 2,650,448 $ 2,695,065 The following table summarizes our depreciation expense: For the Year Ended December 31, 2018 2017 2016 (In thousands) Depreciation expense $ 570,304 $ 580,172 $ 552,989

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Summarized Accrued expenses	Accrued expenses consist of the following: December 31, 2018 2017 (In thousands) Payroll and benefits $ 124,943 $ 134,785 Income taxes payable 38,567 56,664 Deferred revenue and customer advances 16,736 14,740 Accrued severance plan obligations (Note 12) 13,179 15,190 Accrued interest 10,302 11,873 Accrued settlement costs — 37,783 Other accrued expenses 54,482 59,833 Total accrued expenses $ 258,209 $ 330,868

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 (In thousands) Debt of Amkor Technology, Inc.: Senior notes: 6.625% Senior notes, due June 2021 (1) $ — $ 200,000 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 September 2018 (2) — 75,000 $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019 (3) — — Term loan, LIBOR plus 2.70%, due December 2019 — 55,000 Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 (2) — 150,000 Term loan, fixed rate at 3.70%, due May 2020 120,000 120,000 Term loan, fund floating rate plus 1.60%, due June 2020 (4) 125,000 86,000 Term loan, LIBOR plus 2.56%, due December 2023 (2) 200,000 — Term loan, applicable bank rate plus 1.98%, due December 2028 (4) 24,000 — J-Devices Corporation: Short-term term loans, variable rate (5) 8,232 30,455 Term loans, fixed rate at 0.53%, due April 2018 — 6,744 Term loan, fixed rate at 0.86%, due June 2022 31,908 39,933 Term loan, fixed rate at 0.60%, due July 2022 6,838 8,430 Term loan, fixed rate at 1.30%, due July 2023 (1) 225,180 — Other: $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore) (6) — — Revolving credit facility, TAIFX plus the applicable bank rate, due November 2020 (Taiwan) (7) 20,000 20,000 Term loan, LIBOR plus 1.80%, due December 2019 (China) 48,000 49,000 1,334,129 1,365,533 Less: Unamortized premium and deferred debt costs, net (1,818 ) (1,104 ) Less: Short-term borrowings and current portion of long-term debt (114,579 ) (123,848 ) Long-term debt $ 1,217,732 $ 1,240,581 (1) In August 2018, we redeemed all $200 million of our 6.625% Senior Notes due 2021 ("Notes"). In accordance with the terms of the indenture governing the Notes, the redemption price was 100% of the principal amount of the Notes, plus accrued and unpaid interest. We recorded a $0.8 million charge for the write-off of the associated unamortized debt issuance costs. The redemption of the Notes was funded with proceeds from our ¥26.0 billion ( $233.2 million ) term loan agreement entered into in July 2018 by J-Devices Corporation and guaranteed by Amkor Technology, Inc. Principal is payable in quarterly installments. (2) In June 2018, we extended our $75.0 million credit facility from June 2018 to September 2018 and in September 2018, we replaced it with a $75.0 million term loan due September 2021 at LIBOR plus 2.34% . In December 2018, we entered into a $200.0 million term loan agreement to repay this $75.0 million term loan. The remaining proceeds along with cash on hand were used to repay the $141 million outstanding term loan due May 2020. Principal of the new term loan is payable at maturity date of December 2023. (3) In October 2018, we entered into a revolving credit facility agreement with availability of $30.0 million . Principal will be payable at the maturity date of October 2019. As of December 31, 2018 , $30.0 million was available to be drawn. (4) 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 in June 2020. Interest is payable quarterly in arrears. In the second quarter of 2018, we borrowed the remaining $64.0 million available under the term loan due June 2020 and repaid $55 million of the term loan due December 2019 and $9 million of the term loan due May 2020. In December 2018, we entered into a term loan agreement pursuant to which we may borrow up to $90.0 million for capital expenditures. We borrowed $24.0 million of this new term loan and used the proceeds along with $1.0 million cash on hand to repay part of the term loan due June 2020. Principal of the new term loan is payable in semiannual installments beginning June 2022 and ending at maturity date of December 2028. As of December 31, 2018 , $66.0 million was available to be drawn. In February 2019, we borrowed an additional $30.0 million of this new term loan and used the proceeds to repay $29.0 million of the term loan due June 2020. (5) We entered into various short-term loans which mature semiannually. Principal is payable in monthly installments. As of December 31, 2018 , $4.6 million was available to be drawn. (6) In July 2018, the senior secured revolving credit facility of Amkor Technology, Inc. was terminated and replaced by a new facility entered into by our subsidiary, Amkor Technology Singapore Holding Pte, Ltd., and guaranteed by Amkor Technology, Inc. We recorded a $0.4 million charge for the write-off of the associated unamortized debt issuance costs relating to the terminated credit facility. The availability for the new revolving credit facility is based on the amount of eligible accounts receivable. As of December 31, 2018 , we had availability of $250.0 million under the new senior secured revolving credit facility with no outstanding standby letters of credit. (7) In November 2015, we entered into a $39.0 million revolving credit facility. Principal is payable at maturity. As of December 31, 2018 , $19.0 million was available to be drawn.
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, 2018 2017 Amkor Technology Korea, Inc.: $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due September 2018 — 4.01 % $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019 — — Term loan, LIBOR plus 2.70%, due December 2019 — 4.02 % Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 — 4.06 % Term Loan, fund floating rate plus 1.60%, due June 2020 4.49 % 3.29 % Term loan, LIBOR plus 2.56%, due December 2023 5.38 % — Term loan, applicable bank rate plus 1.98%, due December 2028 4.64 % — J-Devices Corporation: Short-term term loans, variable rate 0.24 % 0.22 % Amkor Technology Singapore Holdings Pte, Ltd.: $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 — — Amkor Technology Taiwan Ltd.: Revolving credit facility, TAIFX plus the applicable bank rate, due November 2020 4.26 % 3.18 % Amkor Assembly & Test (Shanghai) Co., Ltd.: Term loan, LIBOR plus 1.80%, due December 2019 4.22 % 3.16 %
Schedule of Maturities of Long-term Debt	Maturities Total Debt (In thousands) Payments due for the year ending December 31, 2019 $ 114,579 2020 323,346 2021 58,346 2022 581,723 2023 238,985 Thereafter 17,150 Total debt $ 1,334,129

Pension and Severance Plans (Ta

Pension and Severance Plans (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 (In thousands) Balance at January 1 $ 153,920 $ 136,396 $ 143,151 Provision of severance benefits 1,939 11,714 6,746 Severance payments (7,611 ) (11,787 ) (9,429 ) Foreign currency (gain) loss (5,950 ) 17,597 (4,072 ) Balance at December 31 142,298 153,920 136,396 Payments remaining with the National Pension Fund (172 ) (185 ) (182 ) Total accrued severance plan obligations at December 31 142,126 153,735 136,214 Less current portion of accrued severance plan obligations (Note 10) 13,179 15,190 14,053 Non-current portion of accrued severance plan obligations $ 128,947 $ 138,545 $ 122,161
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, 2018 and 2017 : For the Year Ended December 31, 2018 2017 (In thousands) Change in projected benefit obligation: Projected benefit obligation at January 1 $ 158,466 $ 131,416 Service cost 32,913 33,823 Interest cost 4,867 4,067 Benefits paid (6,137 ) (15,183 ) Actuarial (gain) loss (5,991 ) (1,387 ) Effects of curtailment — 573 Settlement (5,055 ) (2,496 ) Foreign exchange (gain) loss (3,351 ) 7,653 Projected benefit obligation at December 31 175,712 158,466 Change in plan assets: Fair value of plan assets at January 1 115,725 91,471 Actual gain (loss) on plan assets (4,210 ) 8,559 Employer contributions 26,899 28,073 Settlement (5,055 ) (2,496 ) Benefits paid (6,137 ) (15,183 ) Foreign exchange gain (loss) (3,852 ) 5,301 Fair value of plan assets at December 31 123,370 115,725 Funded status of the Plans at December 31 $ (52,342 ) $ (42,741 )
Schedule of Amounts Recognized in Balance Sheet	December 31, 2018 2017 (In thousands) Amounts recognized in the Consolidated Balance Sheets consist of: Prepaid benefit cost (included in non-current assets) $ 2,740 $ 656 Accrued benefit liability (included in pension and severance obligations) (55,082 ) (43,397 ) Net amount recognized at year end $ (52,342 ) $ (42,741 )
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, 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 Amortization and settlement gain included in net periodic pension cost (1 ) (1,735 ) (1,736 ) Net gain (loss) arising during period — (1,908 ) (1,908 ) Adjustments to unrealized components of defined benefit pension plan included in other comprehensive income (loss) (1 ) (3,643 ) (3,644 ) Balance at December 31, 2018 $ 602 $ 2,057 $ 2,659 Estimated amortization of cost to be included in 2019 net periodic pension cost $ — $ (374 ) $ (374 )
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, 2018 2017 (In thousands) Plans with underfunded or non-funded projected benefit obligation: Aggregate projected benefit obligation $ 135,967 $ 119,708 Aggregate fair value of plan assets 80,885 76,313 Plans with underfunded or non-funded accumulated benefit obligation: Aggregate accumulated benefit obligation 63,274 53,720 Aggregate fair value of plan assets 20,094 18,970
Components of net periodic pension cost	The following table summarizes total pension expense: For the Year Ended December 31, 2018 2017 2016 (In thousands) Components of net periodic pension cost and total pension expense: Service cost $ 32,913 $ 33,823 $ 33,854 Interest cost 4,867 4,067 3,641 Expected return on plan assets (5,640 ) (4,537 ) (3,788 ) Amortization of prior service cost 6 30 35 Recognized actuarial (gain) loss (147 ) 84 94 Net periodic pension cost 31,999 33,467 33,836 Curtailment loss — 574 — Settlement (gain) loss (1,639 ) 383 128 Total pension expense $ 30,360 $ 34,424 $ 33,964
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, 2018 2017 2016 Discount rate for determining net periodic pension cost 3.2 % 3.1 % 3.3 % Discount rate for determining benefit obligations at December 31 3.1 % 3.2 % 3.1 % Rate of compensation increase for determining net periodic 3.8 % 3.8 % 3.9 % Rate of compensation increase for determining benefit obligations 3.6 % 3.8 % 3.8 % Expected rate of return on plan assets for determining net periodic 4.9 % 4.9 % 5.0 %
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 33 % 63 % 4 % The fair value of our pension plan assets, by asset category utilizing the fair value hierarchy as discussed in Note 14 , is as follows: December 31, 2018 2017 (In thousands) Cash and cash equivalents (Level 1) $ 6,640 $ 1,098 Equity securities U.S. securities (Level 1) 15,069 16,854 Foreign securities (Level 1) 10,162 16,826 Foreign mutual funds (Level 1) 25,236 22,193 50,467 55,873 Debt securities U.S. government bonds (Level 1) — 2,188 U.S. government bonds (Level 2) 1,039 830 U.S. corporate bonds (Level 1) — 2,144 U.S. corporate bonds (Level 2) 29 5 Foreign government bonds (Level 1) 4,427 5,211 Foreign government bonds (Level 2) 9,545 6,270 Foreign corporate bonds (Level 1) 5,713 520 Foreign corporate bonds (Level 2) 1,951 3,058 Foreign treasury notes (Level 1) 2,587 4,686 Foreign mutual funds (Level 1) 11,188 8,787 36,479 33,699 Foreign guaranteed investment contracts (Level 2) 18,120 14,138 Taiwan retirement fund (Level 1) 10,451 10,094 Other (Level 1) 680 584 Other (Level 2) 533 239 Total fair value of pension plan assets $ 123,370 $ 115,725
Schedule of Expected Benefit Payments	The estimated future benefit payments related to our foreign defined benefit plans are as follows: Payments (In thousands) 2019 $ 7,922 2020 10,369 2021 12,229 2022 14,979 2023 16,341 2024 to 2028 129,703

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2018
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, 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 Other comprehensive income (loss) before reclassifications (1,908 ) 4,937 3,029 Amounts reclassified from accumulated other comprehensive income (loss) (1,736 ) — (1,736 ) Other comprehensive income (loss) (3,644 ) 4,937 1,293 Balance at December 31, 2018 $ 2,659 $ 21,153 $ 23,812

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 (In thousands) Cash equivalent money market funds (Level 1) $ 74,407 $ 121,627 Restricted cash money market funds (Level 1) 2,589 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, 2018 December 31, 2017 Fair Value Carrying Value Fair Value Carrying Value (In thousands) Senior notes (Level 1) $ 526,131 $ 524,978 $ 745,943 $ 723,867 Revolving credit facilities and term loans (Level 2) 803,867 807,333 639,689 640,562 Total financial instruments $ 1,329,998 $ 1,332,311 $ 1,385,632 $ 1,364,429

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Future minimum lease payments under noncancelable leases are as follows: For the Year Ended December 31 Operating Leases Capital Leases (In thousands) 2019 $ 32,461 $ 6,430 2020 24,630 4,555 2021 17,676 4,748 2022 10,942 936 2023 9,008 936 Thereafter 26,070 3,807 Total future minimum lease payments $ 120,787 $ 21,412

Business Segments, Customer C_2

Business Segments, Customer Concentrations and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 2017 2016 (In thousands) Advanced Products $ 2,118,571 $ 1,966,483 $ 1,703,052 Mainstream Products 2,197,895 2,240,548 2,224,797 Total net sales $ 4,316,466 $ 4,207,031 $ 3,927,849 (1) Advanced products include flip chip and wafer-level processing and related test services. (2) Mainstream products include wirebond packaging and related test services. Net sales by end market consist of the following : For the Year Ended December 31, 2018 2017 2016 Communications (smartphones, tablets, handheld devices) 44 % 43 % 42 % Automotive, industrial and other (driver assist, infotainment, safety, performance) 26 % 26 % 26 % Computing (datacenter, infrastructure, PC/laptop, storage) 18 % 18 % 18 % Consumer (set-top boxes, televisions, connected home, personal electronics, visual imaging) 12 % 13 % 14 % Total net sales 100 % 100 % 100 %
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, 2018 2017 2016 (In thousands) Japan $ 1,156,797 $ 1,210,296 $ 1,162,729 Europe, Middle East and Africa 605,932 540,126 490,738 Asia Pacific (excluding Japan) 535,894 837,014 630,837 Total foreign countries 2,298,623 2,587,436 2,284,304 United States 2,017,843 1,619,595 1,643,545 Total net sales $ 4,316,466 $ 4,207,031 $ 3,927,849
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, 2018 2017 (In thousands) China $ 472,858 $ 528,739 Japan 219,373 246,223 Korea 1,213,838 1,131,271 Malaysia 47,491 47,922 Philippines 270,562 309,425 Portugal 63,323 64,578 Taiwan 352,576 356,174 Other foreign countries 170 216 Total foreign countries 2,640,191 2,684,548 United States 10,257 10,517 Total property, plant and equipment, net $ 2,650,448 $ 2,695,065

Quarterly Results (Unaudited) (

Quarterly Results (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 . 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, 2018 (c) Sep 30, 2018 Jun 30, 2018 Mar 31, 2018 Dec 31, 2017 (c) Sep 30, 2017 Jun 30, 2017 (a) Mar 31, 2017 (In thousands, except per share data) Net sales $ 1,081,271 $ 1,144,192 $ 1,065,684 $ 1,025,319 $ 1,150,478 $ 1,148,884 $ 1,008,385 $ 899,284 Gross profit 182,370 200,707 169,717 157,771 224,341 223,888 176,616 136,234 Operating income (b) 75,381 92,703 53,941 36,119 109,018 105,479 172,659 18,384 Income tax (benefit) expense 28,812 14,326 10,631 2,481 (13,613 ) 21,263 33,466 (1,325 ) Net income (loss) 28,894 57,292 33,184 10,195 101,185 60,458 120,030 (13,968 ) Net income (loss) attributable to Amkor 28,295 56,662 32,591 9,544 100,059 59,264 119,013 (14,786 ) Net income (loss) attributable to Amkor per common share: Basic $ 0.12 $ 0.24 $ 0.14 $ 0.04 $ 0.42 $ 0.25 $ 0.50 $ (0.06 ) Diluted $ 0.12 $ 0.24 $ 0.14 $ 0.04 $ 0.42 $ 0.25 $ 0.50 $ (0.06 ) (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. In the fourth quarter of 2018, we recorded a $22.3 million income tax expense to complete the accounting for the impact of the Tax Act, reducing our estimated net tax benefit of $41.6 million from 2017.

Description of Business and S_4

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, 2018USD ($)
Variable Interest Entity [Line Items]
Ownership Percentage	40.00%
Variable Interest Entity, Consolidated, Carrying Amount, Assets	$ 17
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ 0.2

Description of Business and S_5

Description of Business and Summary of Significant Accounting Policies (Other) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Summary of Significant Accounting Policies [Line Items]
Unbilled receivables	$ 89.3	$ 101.9
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

Description of Business and S_6

Description of Business and Summary of Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018
Minimum
Summary of Significant Accounting Policies [Line Items]
Revenue recognition period	14 days
Maximum
Summary of Significant Accounting Policies [Line Items]
Revenue recognition period	21 days

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2016	Dec. 31, 2015
Income Statement:
Net sales	$ 1,081,271	$ 1,144,192	$ 1,065,684	$ 1,025,319	$ 1,150,478	$ 1,148,884	$ 1,008,385	$ 899,284	$ 4,316,466	$ 4,207,031	$ 3,927,849
Cost of sales									3,605,901	3,445,952	3,217,958
Gross Profit	182,370	200,707	169,717	157,771	224,341	223,888	176,616	136,234	710,565	761,079	709,891
Income tax expense	28,812	14,326	10,631	2,481	(13,613)	21,263	33,466	(1,325)	56,250	39,791	51,042
Net income	28,894	57,292	33,184	10,195	101,185	60,458	120,030	(13,968)	129,565	267,705	178,653
Net income attributable to Amkor	$ 28,295	$ 56,662	$ 32,591	$ 9,544	$ 100,059	$ 59,264	$ 119,013	$ (14,786)	$ 127,092	$ 263,550	$ 175,530
Diluted (in dollars per share)	$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.42	$ 0.25	$ 0.50	$ (0.06)	$ 0.53	$ 1.10	$ 0.74
Balance Sheet:
Accounts receivable, net	$ 724,456				$ 798,264				$ 724,456	$ 798,264
Inventories	230,589				213,649				230,589	213,649
Other Assets, Noncurrent	144,178				139,796				144,178	139,796
Accrued expenses	258,209				330,868				258,209	330,868
Other non-current liabilities	79,071				47,823				79,071	47,823
Accumulated deficit	113,189				(13,903)				113,189	(13,903)
Cumulative effect adjustment from standard adoption												$ 14,764
Operating income	$ 75,381	$ 92,703	$ 53,941	$ 36,119	109,018	$ 105,479	$ 172,659	$ 18,384	258,144	405,540	$ 308,587
As Previously Reported
Income Statement:
Net sales										4,186,497	3,893,635
Cost of sales										3,429,224	3,198,158
Gross Profit										757,273	695,477
Income tax expense										38,982	47,853
Net income										264,888	167,304
Net income attributable to Amkor										$ 260,706	$ 164,190
Diluted (in dollars per share)										$ 1.09	$ 0.69
Balance Sheet:
Accounts receivable, net					692,287					$ 692,287
Inventories					326,492					326,492
Other Assets, Noncurrent					146,051					146,051
Accrued expenses					374,598					374,598
Other non-current liabilities					46,144					46,144
Accumulated deficit					(42,851)					(42,851)
Accounting Standards Update 2017-07
Balance Sheet:
Operating income										(600)	$ (100)
Accounting Standards Update 2014-09
Income Statement:
Net sales										4,207,031	3,927,849
Cost of sales										3,445,952	3,217,958
Gross Profit										761,079	709,891
Income tax expense										39,791	51,042
Net income										267,705	178,653
Net income attributable to Amkor										$ 263,550	$ 175,530
Diluted (in dollars per share)										$ 1.10	$ 0.74
Balance Sheet:
Accounts receivable, net					798,264					$ 798,264
Inventories					213,649					213,649
Other Assets, Noncurrent					139,796					139,796
Accrued expenses					330,868					330,868
Other non-current liabilities					47,823					47,823
Accumulated deficit					(13,903)					(13,903)
New Accounting Pronouncement Adjustment | Accounting Standards Update 2014-09
Income Statement:
Net sales										20,534	$ 34,214
Cost of sales										16,728	19,800
Gross Profit										3,806	14,414
Income tax expense										809	3,189
Net income										2,817	11,349
Net income attributable to Amkor										$ 2,844	$ 11,340
Diluted (in dollars per share)										$ 0.01	$ 0.05
Balance Sheet:
Accounts receivable, net					105,977					$ 105,977
Inventories					(112,843)					(112,843)
Other Assets, Noncurrent					(6,255)					(6,255)
Accrued expenses					(43,730)					(43,730)
Other non-current liabilities					1,679					1,679
Accumulated deficit					28,948					28,948
Retained Earnings (Accumulated Deficit)
Income Statement:
Net income attributable to Amkor									$ 127,092	263,550	$ 175,530
Balance Sheet:
Cumulative effect adjustment from standard adoption												$ 14,764
Retained Earnings (Accumulated Deficit) | Accounting Standards Update 2014-09 | Restatement
Balance Sheet:
Cumulative effect adjustment from standard adoption					$ 2,800					$ 2,800	$ 11,300		$ 14,800

Acquisitions (Narrative) (Detai

Acquisitions (Narrative) (Details)	May 22, 2017
Nanium [Member]
Business Acquisition [Line Items]
Percentage of voting interests acquired	100.00%

Share-Based Compensation Plan_2

Share-Based Compensation Plans (Stock Options) (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares Outstanding beginning balance | shares	4,752
Number of Shares Granted | shares	474
Number of Shares Exercised | shares	(148)
Number of Shares Forfeited or expired | shares	(335)
Number of Shares Outstanding ending balance | shares	4,743
Number of Shares Fully vested and expected to vest | shares	4,673
Number of Shares Exercisable | shares	2,634
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	$ 8.86
Weighted Average Exercise Price Per Share Granted (in dollars per share) | $ / shares	9.40
Weighted Average Exercise Price Per Share Exercised (in dollars per share) | $ / shares	7.10
Weighted Average Exercise Price Per Share Forfeited or expired (in dollars per share) | $ / shares	11.40
Weighted Average Exercise Price Per Share Outstanding ending balance (in dollars per share) | $ / shares	8.79
Weighted Average Exercise Price Per Share Fully vested and expected to vest (in dollars per share) | $ / shares	8.77
Weighted Average Exercise Price Per Share Exercisable (in dollars per share) | $ / shares	$ 8.06
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted Average Remaining Contractual Term Outstanding (years)	7 years 25 days
Average Remaining Contractual Term Fully vested and expected to vest (years)	7 years 18 days
Average Remaining Contractual Term Exercisable (years)	6 years 18 days
Aggregate intrinsic value Outstanding ending balance (in dollars) | $	$ 1,443
Aggregate intrinsic value Fully vested and expected to vest (in dollars) | $	1,443
Aggregate intrinsic value Exercisable (in dollars) | $	$ 1,423

Share-Based Compensation Plan_3

Share-Based Compensation Plans (Weighted Average Fair Value) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected life (in years)	6 years 11 days	5 years 7 months 28 days	6 years 5 months 13 days
Risk-free interest rate	2.70%	1.90%	1.50%
Volatility	42.00%	43.00%	48.00%
Dividend yield	0.00%	0.00%	0.00%
Weighted-average grant date fair value per option granted	$ 4.17	$ 4.24	$ 2.89

Share-Based Compensation Plan_4

Share-Based Compensation Plans (Restricted Shares) (Details) - Restricted shares shares in Thousands	12 Months Ended
	Dec. 31, 2018$ / 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	188
Number of Shares Awards granted | shares	35
Number of Shares Awards vested | shares	(76)
Number of Shares Awards forfeited | shares	0
Number of Shares Nonvested ending balance | shares	147
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	$ 10.15
Weighted Average Grant-Date Fair Value Awards granted (in dollars per share) | $ / shares	8.56
Weighted Average Grant-Date Fair Value Awards vested (in dollars per share) | $ / shares	10.43
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	$ 9.63

Share-Based Compensation Plan_5

Share-Based Compensation Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 02, 2008
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 5,018	$ 5,145	$ 3,251
Deferred income tax benefits for stock options and restricted stock	$ 1,000	$ 2,400	$ 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)	7,800,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Unrecognized compensation expense from Restricted Stock	$ 7,500
Weighted-average period of recognition of unrecognized compensation expense	2 years 1 month 28 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	$ 1,100
Weighted-average period of recognition of unrecognized compensation expense	1 year 9 months
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Income and Expenses [Abstract]
Interest income	$ (4,133)	$ (3,215)	$ (1,326)
Foreign currency (gain) loss, net	1,451	11,823	(3,592)
Loss on debt retirement	1,512	4,835	0
Other (income) expense, net	(5,447)	(953)	(827)
Total other (income) expense, net	$ (6,617)	$ 12,490	$ (5,745)

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Net tax benefit from U.S. tax reform		$ (22,284)	$ 41,554	$ 0
Income tax expense from the Tax Act	$ 22,300
Tax benefit from income tax holiday		$ 1,900	$ 6,200	$ 5,600
Benefit from income tax holiday on diluted earnings per share (in dollars per share)		$ 0.01	$ 0.03	$ 0.02
Undistributed earnings of foreign subsidiaries	1,100,000	$ 1,100,000
Transition tax payable	$ 21,800	21,800
Income Tax Examination [Line Items]
Reductions from lapse of statutes of limitations		22	$ 17	$ 105
Foreign
Income Tax Examination [Line Items]
Repatriation of earnings estimated tax impact		91,800
Reductions from lapse of statutes of limitations		$ 2,900

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Geographic sources of income (loss) before income taxes
United States									$ 5,535	$ 26,040	$ (10,880)
Foreign									180,280	281,456	240,575
Income before taxes									185,815	307,496	229,695
Current:
Federal									22,003	0	0
State									39	11	22
Foreign									47,318	81,969	49,577
Current income tax expense (benefit)									69,360	81,980	49,599
Deferred:
Federal									5,468	(34,787)	0
State									2,993	(4,072)	0
Foreign									(21,571)	(3,330)	1,443
Deferred income tax expense (benefit)									(13,110)	(42,189)	1,443
Income tax expense	$ 28,812	$ 14,326	$ 10,631	$ 2,481	$ (13,613)	$ 21,263	$ 33,466	$ (1,325)	$ 56,250	$ 39,791	$ 51,042

Income Taxes (Reconciliation of

Income Taxes (Reconciliation of effective tax rate) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation between statutory rate and income tax provision
U.S. federal statutory income tax rate									$ 39,021	$ 107,623	$ 80,393
State taxes, net of federal benefit									1,677	2,624	850
Foreign income taxed at different rates									6,741	(50,243)	(19,279)
Foreign exchange (loss) gain									(3,797)	29,756	(1,127)
Change in valuation allowance									(12,662)	(6,763)	(7,903)
Adjustments related to prior years									267	3,329	(2,648)
U.S. tax reform (the Tax Act)									22,284	(41,554)	0
Income tax credits generated									(18,106)	(7,296)	(40,301)
Repatriation of foreign earnings and profits									387	719	25,604
Expiration of net operating losses and credits									19,462	166	15,092
Other									976	1,430	361
Income tax expense	$ 28,812	$ 14,326	$ 10,631	$ 2,481	$ (13,613)	$ 21,263	$ 33,466	$ (1,325)	$ 56,250	$ 39,791	$ 51,042

Income Taxes (Components of def

Income Taxes (Components of deferred tax assets and liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Components of Deferred Tax Assets and Liabilities [Abstract]
Net operating loss carryforwards	$ 13,207	$ 53,130
Income tax credits	107,532	23,998
Property, plant and equipment	38,050	35,479
Deferred interest expense	5,415	0
Accrued liabilities	68,402	68,091
Receivable	31,729	32,719
Unrealized foreign exchange loss	1,410	1,924
Other	14,545	12,682
Total deferred tax assets	280,290	228,023
Valuation allowance	(118,560)	(83,251)
Total deferred tax assets net of valuation allowance	161,730	144,772
Property, plant and equipment	14,605	15,754
Deferred gain	11,651	939
Unrealized foreign exchange gain	1,695	8,383
Unbilled receivables	9,515	8,217
Other	5,805	4,566
Total deferred tax liabilities	43,271	37,859
Other assets	118,697	111,353
Other non-current liabilities	(238)	(4,440)
Net deferred tax assets	$ 118,459	$ 106,913

Income Taxes (Valuation allowan

Income Taxes (Valuation allowance) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Valuation Allowance [Line Items]
Total valuation allowance	$ 118,560	$ 83,251
United States
Valuation Allowance [Line Items]
Total valuation allowance	77,580	43,719
Portugal
Valuation Allowance [Line Items]
Total valuation allowance	$ 40,980	$ 39,532

Income Taxes (Net operating los

Income Taxes (Net operating loss carryforwards) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
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	25,272	$ 220,445
U.S. State
Loss Carryforwards and other details [Abstract]
Operating loss carryforwards	108,011	121,095
Foreign
Loss Carryforwards and other details [Abstract]
Operating loss carryforwards	$ 10,686	$ 2,967

Income Taxes (Tax credit carryf

Income Taxes (Tax credit carryforwards) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
U.S. Federal | U.S. Foreign Tax Credits
Tax Credit Carryforward [Line Items]
Tax Credits	$ 84,056	$ 12,637
U.S. Federal | U.S. Other Tax Credits
Tax Credit Carryforward [Line Items]
Tax Credits	1,117	7,104
Foreign
Tax Credit Carryforward [Line Items]
Tax Credits	$ 22,359	$ 4,257

Income Taxes (Unrecognized tax

Income Taxes (Unrecognized tax benefits - rollforward and discussion) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, beginning of period	$ 27,211	$ 23,149	$ 23,332
Additions based on tax positions related to the current year	401	1,419	1,822
Additions for tax positions of prior years	636	2,661	689
Reductions for tax positions of prior years	(2,958)	(1)	(2,589)
Reductions from lapse of statutes of limitations	(22)	(17)	(105)
Balance, end of period	25,268	$ 27,211	$ 23,149
Income tax contingency [Abstract]
Unrecognized tax benefits, period increase (decrease)	1,900
Liability for uncertain tax positions	25,300
Accrued and unpaid interest and penalties	$ 5,300

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dilutive Securities Adjustments [Line Items]
Net income available to Amkor common stockholders									$ 127,092	$ 263,550	$ 175,530
Weighted-average shares outstanding — basic									239,329	238,937	237,416
Effect of dilutive securities:
Weighted-average shares outstanding — diluted									239,741	239,651	238,034
Net income attributable to Amkor per common share:
Basic (in dollars per share)	$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.42	$ 0.25	$ 0.50	$ (0.06)	$ 0.53	$ 1.10	$ 0.74
Diluted (in dollars per share)	$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.42	$ 0.25	$ 0.50	$ (0.06)	$ 0.53	$ 1.10	$ 0.74
Stock Options and Restricted Share Awards [Member]
Effect of dilutive securities:
Stock options and restricted share awards									412	714	618

Earnings Per Share (Antidilutiv

Earnings Per Share (Antidilutive) (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock Options And Restricted Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options and restricted share awards	3,662	3,445	1,135

Factoring of Accounts Receiva_2

Factoring of Accounts Receivable Factoring of Accounts Receivable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Total Factored
Factoring of Accounts Receivable [Line Items]
Accounts Receivable Sold without Recourse	$ 873.9	$ 611.2
Factoring Fees
Factoring of Accounts Receivable [Line Items]
Accounts Receivable Sold without Recourse	$ 7	$ 4.6

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 7,270,623	$ 6,896,008
Less accumulated depreciation and amortization	(4,620,175)	(4,200,943)
Total property, plant and equipment, net	2,650,448	2,695,065
Depreciation expense	570,304	580,172	$ 552,989
Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	222,884	224,894
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	1,523,065	1,384,846
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	5,196,930	4,926,432
Capital lease machinery and equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	25,874	11,859
Software and computer equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	213,440	200,500
Furniture, fixtures and other equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	17,204	15,722
Construction in progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 44,381	$ 104,910

Property, Plant and Equipment_3

Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	May 31, 2017	Nov. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Proceeds from sale of property, plant and equipment			$ 2,841	$ 141,530	$ 45,635
Gain on sale K1 factory			$ (5,310)	$ 2,648	$ (1,390)
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

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Payroll and benefits	$ 124,943	$ 134,785
Income taxes payable	38,567	56,664
Deferred revenue and customer advances	16,736	14,740
Accrued severance plan obligations (Note 12)	13,179	15,190
Accrued interest	10,302	11,873
Accrued settlement costs	0	37,783
Other accrued expenses	54,482	59,833
Total accrued expenses	$ 258,209	$ 330,868

Debt (Long Term Debt) (Details)

Debt (Long Term Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Aug. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total debt	$ 1,334,129		$ 1,365,533
Less: Unamortized premium and deferred debt costs, net	(1,818)		(1,104)
Less: Short-term borrowings and current portion of long-term debt	(114,579)		(123,848)
Long-term debt	1,217,732		1,240,581
6.625% Senior notes, due June 2021 | Senior notes
Debt Instrument [Line Items]
Total debt	0	$ 200,000
6.375% Senior notes, due October 2022 | Senior notes
Debt Instrument [Line Items]
Total debt	524,971		524,971
$250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore) | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Total debt	0		0
Korea | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due September 2018 | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Total debt	0		75,000
Korea | $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019 | Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Total debt	0		0
Korea | Term loan, LIBOR plus 2.70%, due December 2019 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	0		55,000
Korea | Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 (2) | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	0		150,000
Korea | Term loan, fixed rate at 3.70%, due May 2020 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	120,000		120,000
Korea | Term loan, fund floating rate plus 1.60%, due June 2020 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	125,000		86,000
Korea | Term loan, LIBOR plus 2.56%, due December 2023 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	200,000		0
Korea | Term loan, applicable bank rate plus 1.98%, due December 2028 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	24,000		0
Japan | Short-term term loans, variable rates | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	8,232		30,455
Japan | Term loans, fixed rate at 0.53%, due April 2018 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	0		6,744
Japan | Term loan, fixed rate at 0.86%, due June 2022 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	31,908		39,933
Japan | Term loan, fixed rate at 0.60%, due July 2022 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	6,838		8,430
Japan | Term loan, fixed rate at 1.30%, due July 2023 | Subsidiary Term Loans
Debt Instrument [Line Items]
Total debt	225,180		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
Debt Instrument [Line Items]
Total debt	$ 48,000		$ 49,000

Debt (Additional Information) (

Debt (Additional Information) (Details) ¥ in Billions	1 Months Ended			3 Months Ended	12 Months Ended
	Feb. 22, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Oct. 31, 2018USD ($)	Aug. 31, 2018USD ($)	Jul. 31, 2018USD ($)	Jul. 31, 2018JPY (¥)	May 31, 2015USD ($)
Debt Instrument [Line Items]
Repayments of debt		$ 1,000,000			$ 535,738,000	$ 405,269,000	$ 32,078,000
Total debt		1,334,129,000			1,334,129,000	1,365,533,000
China | Term loan, LIBOR plus 1.80% due December 2019
Debt Instrument [Line Items]
Total debt		48,000,000			48,000,000	49,000,000
Senior notes | 6.625% Senior notes, due June 2021
Debt Instrument [Line Items]
Total debt		$ 0			$ 0				$ 200,000,000
Interest rate (as a percent)		6.625%			6.625%				6.625%
Senior notes | 6.375% Senior notes, due October 2022
Debt Instrument [Line Items]
Total debt		$ 524,971,000			$ 524,971,000	524,971,000
Interest rate (as a percent)		6.375%			6.375%
Subsidiary Term Loans | Korea | Term loan, LIBOR plus 2.70%, due December 2019
Debt Instrument [Line Items]
Repayments of debt				$ 55,000,000
Total debt		$ 0			$ 0	55,000,000
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 (2)
Debt Instrument [Line Items]
Repayments of debt		141,000,000		$ 9,000,000
Total debt		0			$ 0	150,000,000
Interest rate spread (as a percent)					1.32%
Subsidiary Term Loans | Korea | Term loan, fixed rate at 3.70%, due May 2020
Debt Instrument [Line Items]
Total debt		$ 120,000,000			$ 120,000,000	120,000,000
Interest rate (as a percent)		3.70%			3.70%
Subsidiary Term Loans | Korea | Term loan, fund floating rate plus 1.60%, due June 2020
Debt Instrument [Line Items]
Repayments of debt	$ 29,000,000
Credit facility, borrowing capacity												$ 150,000,000
Total debt		$ 125,000,000			$ 125,000,000	86,000,000
Interest rate spread (as a percent)					1.60%
Subsidiary Term Loans | Korea | Term loan, LIBOR plus 2.56%, due December 2023
Debt Instrument [Line Items]
Total debt		200,000,000			$ 200,000,000	0
Amount of debt agreement		200,000,000			200,000,000
Subsidiary Term Loans | Korea | Term loan, applicable bank rate plus 1.98%, due December 2028
Debt Instrument [Line Items]
Credit facility, borrowing capacity		90,000,000			90,000,000
Total debt		24,000,000			24,000,000	0
Remaining borrowing capacity		66,000,000			66,000,000
Subsidiary Term Loans | Korea | Term loan, LIBOR plus 2.34%, due September 2021
Debt Instrument [Line Items]
Interest rate spread (as a percent)			2.34%
Amount of debt agreement			$ 75,000,000
Subsidiary Term Loans | Japan | Term loans, fixed rate at 0.53%, due April 2018
Debt Instrument [Line Items]
Total debt		$ 0			$ 0	6,744,000
Interest rate (as a percent)		0.53%			0.53%
Subsidiary Term Loans | Japan | Term loan, fixed rate at 0.86%, due June 2022
Debt Instrument [Line Items]
Total debt		$ 31,908,000			$ 31,908,000	39,933,000
Interest rate (as a percent)		0.86%			0.86%
Subsidiary Term Loans | Japan | Term loan, fixed rate at 0.60%, due July 2022
Debt Instrument [Line Items]
Total debt		$ 6,838,000			$ 6,838,000	8,430,000
Interest rate (as a percent)		0.60%			0.60%
Subsidiary Term Loans | Japan | Term loan, fixed rate at 1.30%, due July 2023
Debt Instrument [Line Items]
Total debt		$ 225,180,000			$ 225,180,000	0
Interest rate (as a percent)		1.30%			1.30%
Amount of debt agreement										$ 233,200,000	¥ 26
Revolving Credit Facility | Line of Credit | $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore)
Debt Instrument [Line Items]
Credit facility, borrowing capacity		$ 250,000,000			$ 250,000,000
Total debt		0			0	0
Remaining borrowing capacity		$ 250,000,000			$ 250,000,000
Revolving Credit Facility | Line of Credit | $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore) | Minimum
Debt Instrument [Line Items]
Interest rate (as a percent)		1.25%			1.25%
Revolving Credit Facility | Line of Credit | $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore) | Maximum
Debt Instrument [Line Items]
Interest rate (as a percent)		1.75%			1.75%
Revolving Credit Facility | Line of Credit | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due September 2018
Debt Instrument [Line Items]
Credit facility, borrowing capacity			$ 75,000,000
Revolving Credit Facility | Line of Credit | Korea | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due September 2018
Debt Instrument [Line Items]
Credit facility, borrowing capacity		$ 75,000,000			$ 75,000,000
Total debt		0			$ 0	75,000,000
Interest rate spread (as a percent)					1.60%
Revolving Credit Facility | Line of Credit | Korea | $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019
Debt Instrument [Line Items]
Credit facility, borrowing capacity		30,000,000			$ 30,000,000			$ 30,000,000
Total debt		0			0	$ 0
Remaining borrowing capacity		$ 30,000,000			$ 30,000,000
London Interbank Offered Rate (LIBOR) | China | Term loan, LIBOR plus 1.80% due December 2019
Debt Instrument [Line Items]
Interest rate spread (as a percent)					1.80%
London Interbank Offered Rate (LIBOR) | Subsidiary Term Loans | Korea | Term loan, LIBOR plus 2.56%, due December 2023
Debt Instrument [Line Items]
Interest rate spread (as a percent)					2.56%
London Interbank Offered Rate (LIBOR) | Subsidiary Term Loans | Korea | Term loan, applicable bank rate plus 1.98%, due December 2028
Debt Instrument [Line Items]
Interest rate spread (as a percent)					1.98%
Subsequent Event [Member] | Subsidiary Term Loans | Korea | Term loan, applicable bank rate plus 1.98%, due December 2028
Debt Instrument [Line Items]
Total debt	$ 30,000,000

Debt (Narrative) (Details)

Debt (Narrative) (Details) ¥ in Billions	1 Months Ended		3 Months Ended	12 Months Ended
	Aug. 31, 2018USD ($)	Jul. 31, 2018USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Oct. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jul. 31, 2018JPY (¥)	Nov. 30, 2015USD ($)	May 31, 2015USD ($)
Debt Instrument [Line Items]
Total debt				$ 1,334,129,000	$ 1,365,533,000
Debt Instruments [Abstract]
Proceeds from revolving credit facilities				0	75,000,000	$ 125,000,000
Senior notes | 6.625% Senior notes, due June 2021
Debt Instrument [Line Items]
Total debt	$ 200,000,000			$ 0
Debt Instruments [Abstract]
Interest rate (as a percent)	6.625%			6.625%
Redemption price (as a percent)		100.00%
Write off of deferred debt issuance cost	$ 800,000
Line of Credit | Revolving Credit Facility | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due September 2018
Debt Instruments [Abstract]
Credit facility, borrowing capacity								$ 75,000,000
Line of Credit | Revolving Credit Facility | $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
Line of Credit | Revolving Credit Facility | $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore)
Debt Instrument [Line Items]
Total debt				$ 0	0
Debt Instruments [Abstract]
Credit facility, borrowing capacity				250,000,000
Remaining borrowing capacity				250,000,000
Write off of deferred debt issuance cost		$ 400,000
Line of Credit | Revolving Credit Facility | Korea | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due September 2018
Debt Instrument [Line Items]
Total debt				0	75,000,000
Debt Instruments [Abstract]
Credit facility, borrowing capacity				75,000,000
Line of Credit | Revolving Credit Facility | Korea | $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019
Debt Instrument [Line Items]
Total debt				0	0
Debt Instruments [Abstract]
Credit facility, borrowing capacity				30,000,000			$ 30,000,000
Remaining borrowing capacity				30,000,000
Line of Credit | Revolving Credit Facility | Taiwan | Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 (Taiwan)
Debt Instrument [Line Items]
Total debt				20,000,000	20,000,000
Debt Instruments [Abstract]
Credit facility, borrowing capacity										$ 39,000,000
Remaining borrowing capacity				19,000,000
Subsidiary Term Loans | Korea | Term loan, LIBOR plus 2.34%, due September 2021
Debt Instruments [Abstract]
Amount of debt agreement								$ 75,000,000
Subsidiary Term Loans | Korea | Term loan, fund floating rate plus 1.60%, due June 2020
Debt Instrument [Line Items]
Total debt				125,000,000	86,000,000
Debt Instruments [Abstract]
Credit facility, borrowing capacity											$ 150,000,000
Proceeds from revolving credit facilities			$ 64,000,000
Subsidiary Term Loans | Korea | Term loan, LIBOR plus 2.56%, due December 2023
Debt Instrument [Line Items]
Total debt				200,000,000	0
Debt Instruments [Abstract]
Amount of debt agreement				200,000,000
Subsidiary Term Loans | Korea | Term loan, applicable bank rate plus 1.98%, due December 2028
Debt Instrument [Line Items]
Total debt				24,000,000	0
Debt Instruments [Abstract]
Credit facility, borrowing capacity				90,000,000
Remaining borrowing capacity				66,000,000
Subsidiary Term Loans | Japan | Term loan, fixed rate at 1.30%, due July 2023
Debt Instrument [Line Items]
Total debt				$ 225,180,000	0
Debt Instruments [Abstract]
Amount of debt agreement		$ 233,200,000							¥ 26
Interest rate (as a percent)				1.30%
Subsidiary Term Loans | Japan | Short-term term loans, variable rates
Debt Instrument [Line Items]
Total debt				$ 8,232,000	$ 30,455,000
Debt Instruments [Abstract]
Remaining borrowing capacity				$ 4,600,000

Debt (Interest Rates) (Details)

Debt (Interest Rates) (Details)	Dec. 31, 2018	Dec. 31, 2017
Term loan, LIBOR plus 1.80% due December 2019 | China
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	4.22%	3.16%
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)	0.00%	4.02%
Subsidiary Term Loans | Term loan, foreign currency funding-linked base rate plus 1.32%, due May 2020 (2) | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	4.06%
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)	4.49%	3.29%
Subsidiary Term Loans | Term loan, LIBOR plus 2.56%, due December 2023 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	5.38%	0.00%
Subsidiary Term Loans | Term loan, applicable bank rate plus 1.98%, due December 2028 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	4.64%	0.00%
Revolving Credit Facility | Line of Credit | $75 million revolving credit facility, foreign currency funding-linked base rate plus 1.60%, due September 2018 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	4.01%
Revolving Credit Facility | Line of Credit | $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019 | Korea
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	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)	0.24%	0.22%
Revolving Credit Facility | Line of Credit | $250 million senior secured revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore)
Debt Instrument [Line Items]
Interest rate at end of period (as a percent)	0.00%	0.00%
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)	4.26%	3.18%

Debt (Maturities) (Details)

Debt (Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
2,019	$ 114,579
2,020	323,346
2,021	58,346
2,022	581,723
2,023	238,985
Thereafter	17,150
Total debt	$ 1,334,129	$ 1,365,533

Pension and Severance Plans (Ko

Pension and Severance Plans (Korean Severance Plan) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Liability, Current and Noncurrent [Roll Forward]
Total accrued severance plan obligations at December 31	$ 142,126	$ 153,735	$ 136,214
Less current portion of accrued severance plan obligations (Note 10)	13,179	15,190	14,053
Non-current portion of accrued severance plan obligations	128,947	138,545	122,161
Korean Severance Plan
Deferred Compensation Liability, Current and Noncurrent [Roll Forward]
Balance at January 1	153,920	136,396	143,151
Provision of severance benefits	1,939	11,714	6,746
Severance payments	(7,611)	(11,787)	(9,429)
Foreign currency (gain) loss	(5,950)	17,597	(4,072)
Balance at the end of year	142,298	153,920	136,396
Payments remaining with the National Pension Fund	$ (172)	$ (185)	$ (182)

Pension and Severance Plans (De

Pension and Severance Plans (Defined Benefit Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in projected benefit obligation:
Projected benefit obligation at January 1	$ 158,466	$ 131,416
Service cost	32,913	33,823	$ 33,854
Interest cost	4,867	4,067	3,641
Benefits paid	(6,137)	(15,183)
Actuarial (gain) loss	(5,991)	(1,387)
Effects of curtailment	0	573
Settlement	(5,055)	(2,496)
Foreign exchange (gain) loss	(3,351)	7,653
Projected benefit obligation at December 31	175,712	158,466	131,416
Change in plan assets:
Fair value of plan assets at January 1	115,725	91,471
Actual gain (loss) on plan assets	(4,210)	8,559
Employer contributions	26,899	28,073
Settlement	(5,055)	(2,496)
Benefits paid	(6,137)	(15,183)
Foreign exchange gain (loss)	(3,852)	5,301
Fair value of plan assets at December 31	123,370	115,725	$ 91,471
Funded status of the Plans at December 31	(52,342)	(42,741)
Defined Benefit Plan, Liability
Accumulated benefit obligation	132,900	113,600
Defined Benefit Plan, Pension Plan with Project Benefit Obligation in Excess of Plan Assets [Abstract]
Aggregate projected benefit obligation	135,967	119,708
Aggregate fair value of plan assets	80,885	76,313
Defined Benefit Plan, Plan with Accumulated Benefit Obligation in Excess of Plan Assets [Abstract]
Aggregate accumulated benefit obligation	63,274	53,720
Aggregate fair value of plan assets	$ 20,094	$ 18,970
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)	3.20%	3.10%	3.30%
Discount rate for determining benefit obligations at December 31 (as a percent)	3.10%	3.20%	3.10%
Rate of compensation increase for determining net periodic pension cost (as a percent)	3.80%	3.80%	3.90%
Rate of compensation increase for determining benefit obligations at December 31 (as a percent)	3.60%	3.80%	3.80%
Expected rate of return on plan assets for determining net periodic pension cost (as a percent)	4.90%	4.90%	5.00%

Pension and Severance Plans (_2

Pension and Severance Plans (Defined Benefit Plans - Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Prepaid benefit cost (included in non-current assets)	$ 2,740	$ 656
Accrued benefit liability (included in pension and severance obligations)	(55,082)	(43,397)
Net amount recognized at year end	$ (52,342)	$ (42,741)

Pension and Severance Plans (Im

Pension and Severance Plans (Impact on Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Balance at beginning of period	$ 1,719,709	$ 1,429,517	$ 1,217,536
Total other comprehensive income (loss)	1,293	16,257	8,346
Balance at end of period	1,855,900	1,719,709	1,429,517
Prior Service Cost
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Balance at beginning of period	603	582
Amortization and settlement gain included in net periodic pension cost	(1)	21
Net gain (loss) arising during period	0	0
Total other comprehensive income (loss)	(1)	21
Balance at end of period	602	603	582
Estimated amortization of cost to be included in 2019 net periodic pension cost	0
Actuarial Net Gain (Loss)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Balance at beginning of period	5,700	556
Amortization and settlement gain included in net periodic pension cost	(1,735)	69
Net gain (loss) arising during period	(1,908)	5,075
Total other comprehensive income (loss)	(3,643)	5,144
Balance at end of period	2,057	5,700	556
Estimated amortization of cost to be included in 2019 net periodic pension cost	(374)
Total
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [Abstract]
Balance at beginning of period	6,303	1,138
Amortization and settlement gain included in net periodic pension cost	(1,736)	90
Net gain (loss) arising during period	(1,908)	5,075
Total other comprehensive income (loss)	(3,644)	5,165
Balance at end of period	2,659	$ 6,303	$ 1,138
Estimated amortization of cost to be included in 2019 net periodic pension cost	$ (374)

Pension and Severance Plans (Ch

Pension and Severance Plans (Changes and Components) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan [Abstract]
Service cost	$ 32,913	$ 33,823	$ 33,854
Interest cost	4,867	4,067	3,641
Expected return on plan assets	(5,640)	(4,537)	(3,788)
Amortization of prior service cost	6	30	35
Recognized actuarial (gain) loss	(147)	84	94
Net periodic pension cost	31,999	33,467	33,836
Curtailment loss	0	574	0
Settlement (gain) loss	(1,639)	383	128
Total pension expense	$ 30,360	$ 34,424	$ 33,964

Pension and Severance Plans (_3

Pension and Severance Plans (Defined Benefit Plans - Allocation of plan assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 123,370	$ 115,725	$ 91,471
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	50,467	55,873
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	36,479	33,699
Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,640	1,098
Level 1 | US Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15,069	16,854
Level 1 | Foreign Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10,162	16,826
Level 1 | Foreign Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,236	22,193
Level 1 | US Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	2,188
Level 1 | U.S. Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	2,144
Level 1 | Foreign Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,427	5,211
Level 1 | Foreign Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,713	520
Level 1 | Foreign Treasury Notes [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,587	4,686
Level 1 | Foreign Mutual Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,188	8,787
Level 1 | Taiwan Retirement Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10,451	10,094
Level 1 | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	680	584
Level 2 | US Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,039	830
Level 2 | U.S. Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29	5
Level 2 | Foreign Government Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9,545	6,270
Level 2 | Foreign Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,951	3,058
Level 2 | Foreign Guaranteed Investment Contract [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18,120	14,138
Level 2 | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 533	$ 239
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)	63.00%
Philippines | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	33.00%
Philippines | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets, target allocation (as a percent)	4.00%

Pension and Severance Plans (_4

Pension and Severance Plans (Defined Benefit Plans - Expected future contributions and other disclosures) (Details) $ in Thousands	Dec. 31, 2018USD ($)
Defined Benefit Plan [Abstract]
Expected contributions in next fiscal year	$ 23,000
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
2,019	7,922
2,020	10,369
2,021	12,229
2,022	14,979
2,023	16,341
2024 to 2028	$ 129,703

Pension and Severance Plans (_5

Pension and Severance Plans (Defined Contribution Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan [Abstract]
Cost recognized	$ 12.2	$ 10.4	$ 8.8

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,719,709	$ 1,429,517	$ 1,217,536
Total other comprehensive income (loss)	1,293	16,257	8,346
Balance at end of period	1,855,900	1,719,709	1,429,517
Defined Benefit Pension
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	6,303	1,138
Other comprehensive income (loss) before reclassifications	(1,908)	5,075
Amounts reclassified from accumulated other comprehensive income (loss)	(1,736)	90
Total other comprehensive income (loss)	(3,644)	5,165
Balance at end of period	2,659	6,303	1,138
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	16,216	5,124
Other comprehensive income (loss) before reclassifications	4,937	11,092
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Total other comprehensive income (loss)	4,937	11,092
Balance at end of period	21,153	16,216	5,124
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	22,519	6,262
Other comprehensive income (loss) before reclassifications	3,029	16,167
Amounts reclassified from accumulated other comprehensive income (loss)	(1,736)	90
Total other comprehensive income (loss)	1,293	16,257
Balance at end of period	$ 23,812	$ 22,519	$ 6,262

Fair Value Measurements (Detail

Fair Value Measurements (Details) - Recurring - Level 1 - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair value assets measured on recurring basis
Cash equivalent money market funds (Level 1)	$ 74,407	$ 121,627
Restricted cash money market funds (Level 1)	$ 2,589	$ 2,000

Fair Value Measurements (Debt)

Fair Value Measurements (Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	$ 1,329,998	$ 1,385,632
Senior notes (Level 1) | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	526,131	745,943
Revolving credit facilities and term loans (Level 2) | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	803,867	639,689
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	1,332,311	1,364,429
Carrying Value | Senior notes (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	524,978	723,867
Carrying Value | Revolving credit facilities and term loans (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	$ 807,333	$ 640,562

Commitments and Contingencies_2

Commitments and Contingencies (Details) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2015USD ($)payment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Rent expense		$ 43.6	$ 48.1	$ 43.8
Non-lease long-term supply contract, remaining amount		$ 10.4
Patent License Litigation
Loss Contingencies [Line Items]
Amount awarded to other party	$ 155
Number of quarterly settlement payments | payment	16

Commitments and Contingencies_3

Commitments and Contingencies (Future minimum lease payments) (Details) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases
2,019	$ 32,461
2,020	24,630
2,021	17,676
2,022	10,942
2,023	9,008
Thereafter	26,070
Total future minimum lease payments	120,787
Capital Leases
2,019	6,430
2,020	4,555
2,021	4,748
2,022	936
2,023	936
Thereafter	3,807
Total future minimum lease payments	$ 21,412

Business Segments, Customer C_3

Business Segments, Customer Concentrations and Geographic Information (Business Segments) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment									1
Net sales	$ 1,081,271	$ 1,144,192	$ 1,065,684	$ 1,025,319	$ 1,150,478	$ 1,148,884	$ 1,008,385	$ 899,284	$ 4,316,466	$ 4,207,031	$ 3,927,849
Property, plant and equipment, net	2,650,448				2,695,065				2,650,448	2,695,065
Japan
Segment Reporting Information [Line Items]
Net sales									1,156,797	1,210,296	1,162,729
Property, plant and equipment, net	219,373				246,223				219,373	246,223
Europe, Middle East and Africa
Segment Reporting Information [Line Items]
Net sales									605,932	540,126	490,738
Asia Pacific
Segment Reporting Information [Line Items]
Net sales									535,894	837,014	630,837
Total foreign countries
Segment Reporting Information [Line Items]
Net sales									2,298,623	2,587,436	2,284,304
Property, plant and equipment, net	2,640,191				2,684,548				2,640,191	2,684,548
United States
Segment Reporting Information [Line Items]
Net sales									2,017,843	1,619,595	$ 1,643,545
Property, plant and equipment, net	10,257				10,517				10,257	10,517
China
Segment Reporting Information [Line Items]
Property, plant and equipment, net	472,858				528,739				472,858	528,739
Korea
Segment Reporting Information [Line Items]
Property, plant and equipment, net	1,213,838				1,131,271				1,213,838	1,131,271
Malaysia
Segment Reporting Information [Line Items]
Property, plant and equipment, net	47,491				47,922				47,491	47,922
Philippines
Segment Reporting Information [Line Items]
Property, plant and equipment, net	270,562				309,425				270,562	309,425
Portugal
Segment Reporting Information [Line Items]
Property, plant and equipment, net	63,323				64,578				63,323	64,578
Taiwan
Segment Reporting Information [Line Items]
Property, plant and equipment, net	352,576				356,174				352,576	356,174
Other foreign countries
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 170				$ 216				$ 170	$ 216
Sales | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Concentration risk (as a percent)									100.00%	100.00%	100.00%
Customer One | Sales | Customer Concentration Risk
Segment Reporting Information [Line Items]
Concentration risk (as a percent)									10.20%	14.30%	15.70%
Customer Two | Sales | Customer Concentration Risk
Segment Reporting Information [Line Items]
Concentration risk (as a percent)											12.90%
Advanced Products
Segment Reporting Information [Line Items]
Net sales									$ 2,118,571	$ 1,966,483	$ 1,703,052
Mainstream Products
Segment Reporting Information [Line Items]
Net sales									$ 2,197,895	$ 2,240,548	$ 2,224,797
Communications (smartphones, tablets, handheld devices) | Sales | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Concentration risk (as a percent)									44.00%	43.00%	42.00%
Automotive, industrial and other (driver assist, infotainment, safety, performance) | Sales | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Concentration risk (as a percent)									26.00%	26.00%	26.00%
Computing (datacenter, infrastructure, PC/laptop, storage) | Sales | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Concentration risk (as a percent)									18.00%	18.00%	18.00%
Consumer (set-top boxes, televisions, connected home, personal electronics, visual imaging) | Sales | Product Concentration Risk [Member]
Segment Reporting Information [Line Items]
Concentration risk (as a percent)									12.00%	13.00%	14.00%

Quarterly Results (Unaudited)_2

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Net sales			$ 1,081,271	$ 1,144,192	$ 1,065,684	$ 1,025,319	$ 1,150,478	$ 1,148,884	$ 1,008,385	$ 899,284	$ 4,316,466	$ 4,207,031	$ 3,927,849
Gross Profit			182,370	200,707	169,717	157,771	224,341	223,888	176,616	136,234	710,565	761,079	709,891
Operating income			75,381	92,703	53,941	36,119	109,018	105,479	172,659	18,384	258,144	405,540	308,587
Income tax (benefit) expense			28,812	14,326	10,631	2,481	(13,613)	21,263	33,466	(1,325)	56,250	39,791	51,042
Net income (loss)			28,894	57,292	33,184	10,195	101,185	60,458	120,030	(13,968)	129,565	267,705	178,653
Net income (loss) attributable to Amkor			$ 28,295	$ 56,662	$ 32,591	$ 9,544	$ 100,059	$ 59,264	$ 119,013	$ (14,786)	$ 127,092	$ 263,550	$ 175,530
Basic (in dollars per share)			$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.42	$ 0.25	$ 0.50	$ (0.06)	$ 0.53	$ 1.10	$ 0.74
Diluted (in dollars per share)			$ 0.12	$ 0.24	$ 0.14	$ 0.04	$ 0.42	$ 0.25	$ 0.50	$ (0.06)	$ 0.53	$ 1.10	$ 0.74
Condensed Income Statements, Captions [Line Items]
Proceeds from sale of property, plant and equipment											$ 2,841	$ 141,530	$ 45,635
Gain on sale K1 factory											(5,310)	2,648	(1,390)
Net tax benefit from U.S. tax reform											$ (22,284)	$ 41,554	$ 0
Income tax expense from the Tax Act			$ 22,300
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

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Details) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 83,251	$ 165,484	$ 168,762
Additions (Credited) Charged to Expense	54,421	(117,121)	7,189
Write-offs	(19,112)	(489)	(15,091)
Other	0	35,377	4,624
Balance at End of Period	$ 118,560	$ 83,251	$ 165,484

Uncategorized Items - amkr-2018

Label	Element	Value
Parent [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 14,764,000