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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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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 25 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=123466103&loc=SL6014347-161799 + Details
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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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=124435984&loc=d3e28541-108399 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1F -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495355-112611 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.8) -URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227 + Details
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- Definition Amount of amortization expense attributable to debt issuance costs. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(8)) -URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1F -Subparagraph (b)(2) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495355-112611 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399 + Details
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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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870 + Details
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- Definition The price per share of the conversion feature embedded in the debt instrument. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031898-161870 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 + Details
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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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031898-161870 + Details
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