Income Taxes - Classification of Consolidated Balance Sheets on Deferred Tax Balances (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2018 CNY (¥)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 CNY (¥)
Classification in the consolidated balance sheets:
Deferred tax assets, net	¥ 23,873	$ 3,472	¥ 11,380
Deferred tax liabilities	¥ 96,405	$ 14,022	¥ 2,255

Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards classified as noncurrent.

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Name:	us-gaap_DeferredTaxAssetsNetNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant