Short-term investments - Contractual Maturities Of Short-Term Investments Designated As Available-For-Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost, Due in less than 1 year	$ 102,843
Fair Value, Due in less than 1 year	103,239
Adjusted Cost, Due in 1 to 5 years	134,580
Fair Value, Due in 1 to 5 years	134,744
Adjusted Cost	237,423	$ 271,977
Fair Value, Total	237,983	271,396
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	102,843
Fair Value, Due in less than 1 year	103,239
Adjusted Cost, Due in 1 to 5 years	134,580
Fair Value, Due in 1 to 5 years	134,744
Fair Value, Total	$ 237,983	234,473
U.S. Treasuries and agencies
Debt Securities, Available-for-sale [Line Items]
Adjusted Cost		36,932
Fair Value, Total		$ 36,923

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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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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