Commitments and Contingencies - Additional Information (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2018 CNY (¥)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 CNY (¥)	Dec. 31, 2016 CNY (¥)	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Total office rental expenses	¥ 134,634	$ 19,582	¥ 106,740	¥ 85,527
Purchase of fixed assets	101,626				$ 14,781
Accrued expenses	19,067				2,773
Recognized losses	¥ 16,259				$ 2,365

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Amount of loss contingency liability.

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

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Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

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