Income Taxes - Reconciliation of the beginning and ending amount of unrecognized tax benefit (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2021 CNY (¥)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 CNY (¥)	Dec. 31, 2019 CNY (¥)
Reconciliation of the beginning and ending amount of unrecognized tax benefit
Balance at the beginning of the year	¥ 1,430	$ 224	¥ 2,183	¥ 447
Increase	317	50		1,736
Decrease			(753)
Balance at the end of the year	¥ 1,747	$ 274	¥ 1,430	¥ 2,183

Amount of unrecognized tax benefits.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 10B
-URI http://asc.fasb.org/extlink&oid=123427490&loc=SL37586934-109318

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319

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