Short-term investments - Contractual Maturities Of Short-Term Investments Designated As Available-For-Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost, Due in less than 1 year	$ 99,137
Fair Value, Due in less than 1 year	99,500
Adjusted Cost, Due in 1 to 5 years	37,561
Fair Value, Due in 1 to 5 years	37,604
Adjusted Cost	136,698	$ 237,423
Fair Value	137,104	237,983
Carrying value of equity method investments	15,000
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost, Due in less than 1 year	99,137
Fair Value, Due in less than 1 year	99,500
Adjusted Cost, Due in 1 to 5 years	37,561
Fair Value, Due in 1 to 5 years	37,604
Fair Value	$ 137,104	$ 237,983

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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