Foreign exchange rate used to translate amounts denominated in functional currency to reporting currency.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section S99
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6897108&loc=SL6897125-166521

Name:	us-gaap_ForeignCurrencyExchangeRateTranslation1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

Risks and Concentration - Foreign currency exchange rate risks (Details)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Foreign currency exchange rate risk
Convenience translation rate (RMB to USD)	6.9618
RMB
Foreign currency exchange rate risk
Convenience translation rate (RMB to USD)	1.4	5.7	6.3