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Equity Incentive Schemes and Stock Compensation Charges - Outstanding and Exercisable Share Options (Details) - $ / shares | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Minimum Range Exercise Price (USD per share) | $ 14.80 |  |  |
Maximum Range Exercise Price (USD per share) | 231.08 |  |  |
Range 1 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Minimum Range Exercise Price (USD per share) | 14.80 |  |  |
Maximum Range Exercise Price (USD per share) | 97.30 |  |  |
Range 2 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Minimum Range Exercise Price (USD per share) | 103.81 |  |  |
Maximum Range Exercise Price (USD per share) | 124.00 |  |  |
Range 3 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Minimum Range Exercise Price (USD per share) | 125.74 |  |  |
Maximum Range Exercise Price (USD per share) | 147.26 |  |  |
Range 4 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Minimum Range Exercise Price (USD per share) | 159.33 |  |  |
Maximum Range Exercise Price (USD per share) | $ 231.08 |  |  |
Stock Option and Award Plans |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Shares (in shares) | 1,695,460 |  |  |
Weighted Average Remaining Contractual Life | 5 years 4 months 20 days |  |  |
Weighted average exercise price (USD per share) | $ 104.79 | $ 108.53 | $ 87.80 | $ 74.32
Number of Shares (in shares) | 989,419 |  |  |
Vested and exercisable at end of period (USD per share) | $ 91.70 |  |  |
Stock Option and Award Plans | Range 1 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Shares (in shares) | 638,118 |  |  |
Weighted Average Remaining Contractual Life | 3 years 5 months 12 days |  |  |
Number of Shares (in shares) | 605,624 |  |  |
Stock Option and Award Plans | Range 2 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Shares (in shares) | 320,310 |  |  |
Weighted Average Remaining Contractual Life | 6 years 5 months 26 days |  |  |
Number of Shares (in shares) | 130,920 |  |  |
Stock Option and Award Plans | Range 3 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Shares (in shares) | 540,296 |  |  |
Weighted Average Remaining Contractual Life | 6 years 6 months 21 days |  |  |
Number of Shares (in shares) | 235,808 |  |  |
Stock Option and Award Plans | Range 4 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Shares (in shares) | 196,736 |  |  |
Weighted Average Remaining Contractual Life | 6 years 8 months 4 days |  |  |
Number of Shares (in shares) | 17,067 |  |  |

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- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest exercisable or convertible options. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Weighted average remaining contractual term of outstanding stock options, 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 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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