Taxation - Movement of Valuation Allowance (Details) - CNY (¥) ¥ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Taxation
Balance at beginning of the year	¥ (305,974)	¥ (225,250)
Current period addition	(16,799)	(80,724)
Balance at end of the year	¥ (322,773)	¥ (305,974)

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

Name:	us-gaap_DeferredTaxAssetsValuationAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant