Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Expiration date of each operating loss carryforward included in operating loss carryforward, in CCYY-MM-DD format.

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Income tax disclosure.

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Preferential income tax rate.

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Amount of withholding taxes on remittance of dividends.

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Income Tax - Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Taxable income	$ (128,617)	$ (83,274)
Provision for income taxes	$ 0	$ 0
Amounts of operating loss carry forwards			$ 403,460
Earliest Tax Year
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration	Dec. 31, 2020
Latest Tax Year
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration	Dec. 31, 2029
PRC
Income Tax Disclosure [Line Items]
Statutory income tax rate	25.00%	25.00%
Taxable income	$ (112,320)	$ (76,299)
Preferential tax rate	15.00%
Zai Lab (AUST) Pty., Ltd
Income Tax Disclosure [Line Items]
Statutory income tax rate	30.00%
Taxable income	$ 0	0
Provision for income taxes	$ 0	0
Zai Lab (US) LLC
Income Tax Disclosure [Line Items]
Statutory income tax rate	21.00%
Taxable income	$ 0	0
Provision for income taxes		$ 0
Zai Lab (Hong Kong) Limited
Income Tax Disclosure [Line Items]
Provision for income taxes	0
Withholding taxes on remittance of dividends	$ 0
Zai Lab (Hong Kong) Limited \| First two million
Income Tax Disclosure [Line Items]
Statutory income tax rate	8.25%
Zai Lab (Hong Kong) Limited \| Above two million
Income Tax Disclosure [Line Items]
Statutory income tax rate	16.50%
Zai Lab (Shanghai) Co., Ltd
Income Tax Disclosure [Line Items]
Preferential tax rate	15.00%
Zai Lab International Trading (Shanghai) Co., Ltd
Income Tax Disclosure [Line Items]
Statutory income tax rate	25.00%
Zai Lab (Suzhou) Co., Ltd
Income Tax Disclosure [Line Items]
Statutory income tax rate	25.00%
Zai Biopharmaceutical (Suzhou) Co., Ltd
Income Tax Disclosure [Line Items]
Statutory income tax rate	25.00%