Fair value measurements - Summary of Liabilities Measured at Fair Value on Recurring Basis (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2019 USD ($)	Dec. 31, 2019 CNY (¥)	Dec. 31, 2018 CNY (¥)
Assets
Short-term investments	$ 807,577	¥ 5,622,189	¥ 979,053
Recurring [Member]
Assets
Short-term investments		5,622,189	979,053
Equity investment with readily determinable fair values		115,926	238,915
Derivative - forward exchange contracts		6,340
Total		5,744,455	1,217,968
Liabilities
Derivative liabilities		(11,495)
Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets
Short-term investments		481,243	78,605
Equity investment with readily determinable fair values		115,926	238,915
Derivative - forward exchange contracts		0
Total		597,169	317,520
Liabilities
Derivative liabilities		0
Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets
Short-term investments		5,140,946	900,448
Equity investment with readily determinable fair values		0
Derivative - forward exchange contracts		6,340
Total		5,147,286	¥ 900,448
Liabilities
Derivative liabilities		¥ (11,495)

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value portion of investments accounted under the equity method.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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