Cash and cash equivalents and marketable securities (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Cash and cash equivalents:
Cash	$ 4,611		$ 11,689
Money market accounts	59,910		137,723
Marketable securities	4,495		0
Total cash and cash equivalents	69,016		149,412
Short-term marketable securities-available-for-sale:
Marketable securities	36,888		0
Total short-term marketable securities	36,888		$ 0
Interest income	$ 714	$ 8

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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Amount of investment in marketable security, classified as current.

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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