Short-term investments (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019
Schedule Of Available For Sale Securities [Line Items]
Maturities of Time Deposits, Description	the time deposits with original maturities between three months and one year
Time deposits, Interest income	$ 2,512	$ 3,306
Minimum
Schedule Of Available For Sale Securities [Line Items]
Time deposits, Maturity period	3 months
Maximum
Schedule Of Available For Sale Securities [Line Items]
Time deposits, Maturity period	1 year

Interest income derived from funds deposited with both domestic and foreign financial institutions including funds in money market and other accounts.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.4)
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Description of time deposit maturities, including certificates of deposit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
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Period of time between issuance and maturity of customer deposits, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher SEC
-Name Industry Guide
-Number 3
-Section V
-Paragraph D-E

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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