Contractual maturities of cash, cash equivalent and short-term investment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 29,386	$ 25,704
Short-term investments	204,476	204,164
Cash, cash equivalents and short-term investments	233,862	229,868
Maturity up to one year
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	29,386	25,704
Short-term investments	121,605	113,010
Cash, cash equivalents and short-term investments	150,991	138,714
maturity between 1 and 2 years [Member]
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0	0
Short-term investments	82,871	91,154
Cash, cash equivalents and short-term investments	$ 82,871	$ 91,154