Principal Accounting Policies - Sales and marketing expenses (Details) - CNY (¥) ¥ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Sales and marketing expenses
Total advertising and promotion expenses including traffic acquisition expenses	¥ 70.7	¥ 99.9	¥ 314.2

The total expense recognized in the period for promotion, public relations, and brand or product advertising.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.4)
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

Name:	us-gaap_MarketingAndAdvertisingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration