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Convertible debt (Details)		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2021 USD ($)	Sep. 30, 2021 USD ($) $ / shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 293,750,000		$ 293,750,000		$ 293,750,000
Convertible Debt, Noncurrent		287,914,000		287,914,000		218,028,000
Debt Instrument, Fair Value Disclosure		302,200,000		302,200,000		363,800,000
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt			$ 47,215,000		$ 47,215,000
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net		5,836,000		5,836,000		75,722,000
Convertible Debt		287,914,000		287,914,000		218,028,000
Debt Instrument, Convertible, Carrying Amount of Equity Component		0		0		80,098,000
Debt Instrument, Periodic Payment, Interest		1,203,000	500,000	3,609,000	1,219,000
Amortization of Financing Costs		373,000	174,000	1,119,000	488,000
Amortization of Debt Discount (Premium)		0	1,824,000	0	4,938,000
Interest Expense, Debt		1,576,000	$ 2,498,000	4,728,000	6,645,000
Purchase of convertible bond hedge				0	$ 25,335,000
Accounting Standards Update 2020-06
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount and Debt Issuance Cost	$ 68,800,000
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt	$ 80,100,000
Notes due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount		143,750,000		143,750,000
Convertible Debt, Current		0		0
Convertible Debt, Noncurrent		$ 141,433,000		$ 141,433,000
Debt Instrument, Interest Rate, Stated Percentage		1.00%		1.00%
Debt Instrument, Convertible, Conversion Ratio				15.1394
Debt Instrument, Convertible, Stock Price Trigger | $ / shares				$ 66.05
Debt Instrument, Convertible, Remaining Discount Amortization Period				31 months
Debt Instrument, Convertible, Carrying Amount of Equity Component						32,900,000
Convertible debt, issuance cost, equity component						1,100,000
Debt Instrument, Convertible, Conversion Price | $ / shares		$ 101.62		$ 101.62
Purchase of convertible bond hedge				$ 16,400,000
Notes due 2027
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 150,000,000		150,000,000
Convertible Debt, Current		0		0
Convertible Debt, Noncurrent		$ 146,481,000		$ 146,481,000
Debt Instrument, Interest Rate, Stated Percentage		2.25%		2.25%
Debt Instrument, Convertible, Conversion Ratio				23.9137
Debt Instrument, Convertible, Stock Price Trigger | $ / shares				$ 41.82
Debt Instrument, Convertible, Remaining Discount Amortization Period				71 months
Debt Instrument, Convertible, Carrying Amount of Equity Component						47,200,000
Convertible debt, issuance cost, equity component						$ 1,300,000
Debt Instrument, Convertible, Conversion Price | $ / shares		$ 78.90		$ 78.90
Purchase of convertible bond hedge				$ 25,300,000

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Adjustment to additional paid in capital resulting from the recognition of convertible debt instruments as two separate components - a debt component and an equity component. This bifurcation may result in a basis difference associated with the liability component that represents a temporary difference for purposes of applying accounting for income taxes. The initial recognition of deferred taxes for the tax effect of that temporary difference is as an adjustment to additional paid in capital.

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-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495743-112612

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1F
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495355-112611

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