Convertible debt (Details) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2020 USD ($) $ / shares	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 143,750		$ 143,750
Convertible Debt, Noncurrent	112,406		110,704
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	31,344		33,046
Convertible Debt	112,406		110,704
Debt Instrument, Convertible, Carrying Amount of Equity Component	32,883		32,883
Debt Instrument, Periodic Payment, Interest	360	$ 1,250
Amortization of Financing Costs	156	365
Amortization of Debt Discount (Premium)	1,546	2,741
Interest Expense, Debt	2,062	$ 4,356
Debt Instrument, Fair Value Disclosure	121,500		$ 163,200
Purchase of convertible bond hedge	$ 16,400
Notes due 2019 [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Stock Price Trigger \| $ / shares	$ 33.79
Investment Warrants, Exercise Price \| $ / shares	$ 45.48
Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Issuance Cost	$ 3,400
Convertible debt, issuance cost, equity component	$ 1,100
Debt Instrument, Convertible, Conversion Ratio	15.1394
Debt Instrument, Convertible, Stock Price Trigger \| $ / shares	$ 66.05
Debt Instrument, Convertible, Conversion Price \| $ / shares	$ 101.62
Debt Instrument, Face Amount	$ 143,750
Convertible Debt, Current	0
Convertible Debt, Noncurrent	112,406
Debt Instrument, Convertible, Carrying Amount of Equity Component	$ 32,900
Debt Instrument, Convertible, Remaining Discount Amortization Period	49 months
Debt Instrument, Interest Rate, Stated Percentage	1.00%

Convertible debt, issuance cost, equity component

No definition available.

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- Definition

Purchase of capped call

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No definition available.

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- Definition

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount of amortization expense attributable to debt issuance costs.

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Exercise price per share or per unit of warrants or rights outstanding.

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- Definition

Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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The portion of the carrying value of long-term convertible debt as of the balance sheet date that is scheduled to be repaid within one year or in the normal operating cycle if longer. Convertible debt is a financial instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder.

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Carrying amount of long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months or greater than the normal operating cycle, if longer. The debt is convertible into another form of financial instrument, typically the entity's common stock.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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The price per share of the conversion feature embedded in the debt instrument.

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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- Definition

Remaining amortization period for discount on the liability component of convertible debt which may be settled in cash upon conversion, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Price of the entity's common stock which would be required to be attained for the conversion feature embedded in the debt instrument to become effective.

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No definition available.

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Face (par) amount of debt instrument at time of issuance.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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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No definition available.

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Amount of the required periodic payments applied to interest.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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