Fair value of financial instruments and investments - Schedule of financial assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Aug. 23, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	$ 58,088		$ 79,454
Contingent consideration payable	310,240		0
Fair Value, Measurements, Recurring \| Total
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	58,088		79,454
Warrant liability	0		1
Stock appreciation rights liability	3,814		1,665
Deferred consideration payable	37,700
Contingent consideration payable	257,040
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	53,200
Fair Value, Measurements, Recurring \| Quoted prices in active markets for identical assets (level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0		0
Warrant liability	0		0
Stock appreciation rights liability	0		0
Deferred consideration payable	0
Contingent consideration payable	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	0
Fair Value, Measurements, Recurring \| Significant other observable inputs (level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	58,088		79,454
Warrant liability	0		0
Stock appreciation rights liability	0		0
Deferred consideration payable	37,700
Contingent consideration payable	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0		0
Warrant liability	0		1
Stock appreciation rights liability	3,814		$ 1,665
Deferred consideration payable	0
Contingent consideration payable	257,040
Agilis
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred consideration payable		$ 38,100
Agilis \| Significant unobservable inputs (level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	$ 53,200

Business Combination, Consideration, Liability, Deferred Consideration Payable

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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).

+ References

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Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled beyond one year or the normal operating cycle, if longer.

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Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Value of outstanding derivative securities that permit the holder the right to purchase securities (usually equity) from the issuer at a specified price.

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