Debt (Details) - USD ($)	1 Months Ended				3 Months Ended
	Apr. 30, 2019	Mar. 31, 2019	Feb. 28, 2019	Dec. 31, 2016	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018	Feb. 22, 2019	Dec. 31, 2018	Oct. 31, 2018	Jul. 31, 2018	Nov. 30, 2015	May 31, 2015
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 1,862,046,000				$ 1,862,046,000			$ 1,334,129,000
Less: Unamortized premium, discount and deferred debt costs, net		(8,082,000)				(8,082,000)			(1,818,000)
Less: Short-term borrowings and current portion of long-term debt		(638,702,000)				(638,702,000)			(114,579,000)
Long-term debt		1,215,262,000				1,215,262,000			1,217,732,000
Repayments of long-term debt						63,636,000	$ 6,220,000
Term loan, LIBOR plus 1.80%, due December 2019 (China) | China
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		28,000,000				$ 28,000,000			48,000,000
Basis spread on variable rate (as a percent)						1.80%
Face amount of debt				$ 50,000,000
Repayments of long-term debt		$ 20,000,000
Interest rate at period end (as a percent)		4.60%				4.60%
Semiannual installment payments				$ 500,000
Term loan, LIBOR plus 1.80%, due December 2019 (China) | China | Subsequent Event
Debt Instrument [Line Items]
Repayments of long-term debt	$ 28,000,000
Term loan, LIBOR plus 1.80%, due December 2019 (China) | China | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)						1.80%
Term loan, LIBOR plus 1.60%, due March 2022 | China
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 20,000,000				$ 20,000,000			0
Basis spread on variable rate (as a percent)						1.60%
Face amount of debt		30,000,000				$ 30,000,000
Remaining borrowing capacity		$ 10,000,000				$ 10,000,000
Interest rate at period end (as a percent)		4.21%				4.21%
Semiannual installment payments		$ 500,000
Proceeds from revolving credit facilities		20,000,000
Term loan, LIBOR plus 1.60%, due March 2022 | China | Subsequent Event
Debt Instrument [Line Items]
Proceeds from revolving credit facilities	$ 10,000,000
Term loan, LIBOR plus 1.60%, due March 2022 | China | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)						1.60%
Line of Credit | $250 million revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore) | Revolving Credit Facility
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		0				$ 0			0
Credit facility, borrowing capacity		250,000,000.0				250,000,000.0					$ 250,000,000
Remaining borrowing capacity		176,000,000				$ 176,000,000
Line of Credit | $250 million revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore) | Revolving Credit Facility | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)						1.25%
Line of Credit | $250 million revolving credit facility, LIBOR plus 1.25%-1.75%, due July 2023 (Singapore) | Revolving Credit Facility | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)						1.75%
Line of Credit | Revolving credit facility, TAIFX plus a bank-determined spread, due November 2020 (Taiwan) | Revolving Credit Facility | Taiwan
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		20,000,000				$ 20,000,000			20,000,000
Credit facility, borrowing capacity												$ 39,000,000
Remaining borrowing capacity		$ 19,000,000				$ 19,000,000
Interest rate at period end (as a percent)		3.78%				3.78%
Senior Notes | 6.375% Senior notes, due October 2022
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 524,971,000				$ 524,971,000			524,971,000
Stated interest rate (as a percent)		6.375%				6.375%
Face amount of debt		$ 525,000,000				$ 525,000,000
Debt redemption price		101.594%
Senior Notes | 6.375% Senior notes, due October 2022 | Scenario, Forecast
Debt Instrument [Line Items]
Early extinguishment of debt					$ 8,000,000
Senior Notes | 6.625% Senior notes, due September 2027
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 525,000,000				$ 525,000,000			0
Stated interest rate (as a percent)		6.625%				6.625%
Face amount of debt		$ 525,000,000				$ 525,000,000
Debt discount percentage of par		99.50%				99.50%
Debt discount		$ 2,600,000				$ 2,600,000
Debt issuance costs		3,600,000				3,600,000
Subsidiary Term Loans | $30 million revolving credit facility, LIBOR plus the applicable bank rate, due October 2019 (2) | Korea
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		0				0			0
Credit facility, borrowing capacity		30,000,000				30,000,000				$ 30,000,000
Remaining borrowing capacity		30,000,000				30,000,000
Subsidiary Term Loans | Term loan, fund floating rate plus 1.60%, due June 2020 | Korea
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 96,000,000				$ 96,000,000			125,000,000
Basis spread on variable rate (as a percent)						1.60%
Credit facility, borrowing capacity													$ 150,000,000
Repayments of long-term debt			$ 29,000,000
Interest rate at period end (as a percent)		4.70%				4.70%
Subsidiary Term Loans | Term loan, LIBOR plus 2.56%, due December 2023 | Korea
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 200,000,000				$ 200,000,000			200,000,000
Subsidiary Term Loans | Term loan, LIBOR plus 2.56%, due December 2023 | Korea | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)						2.56%
Subsidiary Term Loans | Term loan, applicable bank rate plus 1.98%, due December 2028 | Korea
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		54,000,000				$ 54,000,000			24,000,000
Basis spread on variable rate (as a percent)						1.98%
Credit facility, borrowing capacity									90,000,000
Face amount of debt								$ 30,000,000
Remaining borrowing capacity		$ 36,000,000				$ 36,000,000
Interest rate at period end (as a percent)		4.62%				4.62%
Subsidiary Term Loans | Short-term term loans, variable rate | Japan
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 27,368,000				$ 27,368,000			8,232,000
Remaining borrowing capacity		4,000,000				$ 4,000,000
Subsidiary Term Loans | Short-term term loans, variable rate | Japan | TIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)						0.17%
Subsidiary Term Loans | Short-term term loans, variable rate | Japan | TIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)						0.26%
Subsidiary Term Loans | Short-term term loans, variable rate | Japan | TIBOR | Weighted Average
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)						0.20%
Subsidiary Term Loans | Term loan, fixed rate at 0.86%, due June 2022 | Japan
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 29,316,000				$ 29,316,000			31,908,000
Stated interest rate (as a percent)		0.86%				0.86%
Subsidiary Term Loans | Term loan, fixed rate at 0.60%, due July 2022 | Japan
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 6,314,000				$ 6,314,000			6,838,000
Stated interest rate (as a percent)		0.60%				0.60%
Subsidiary Term Loans | Term Loan, Fixed Rate at 1.30% Due July 2023 | Japan
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 211,077,000				$ 211,077,000			225,180,000
Stated interest rate (as a percent)		1.30%				1.30%
Term Loan | Term loan, fixed rate at 3.70%, due May 2020 | Korea
Debt Instrument [Line Items]
Short-term borrowings and long-term debt		$ 120,000,000				$ 120,000,000			$ 120,000,000
Stated interest rate (as a percent)		3.70%				3.70%
Term Loan | Amkor Assembly & Test (Shanghai) Co., Ltd. Term Loan | China | Subsequent Event
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)	1.40%
Face amount of debt	$ 20,000,000
Semiannual installment payments	$ 500,000
Term of debt instrument	3 years