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Share-based awards - Narrative (Details) - USD ($) |  |  |  |  |  | 6 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 30, 2021 | Dec. 31, 2020 | Feb. 14, 2017 | May 11, 2015 | Jan. 17, 2003 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020 | May 16, 2019 | Feb. 13, 2017
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Non-cash stock compensation expense not yet recognized | $ 72,600,000 |  |  |  |  | $ 72,600,000 |  |  |  |
Unrecognized stock-based compensation expense, weighted average period | 2 years 5 months 1 day |  |  |  |  |  |  |  |  |
Consultants Stock Plan, 2008 Plan |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  |  | 1,000,000.0 |  |  |  |  |  |  | 400,000
Limit of shares issued or to be issued pursuant to options granted (in shares) |  |  | 1,000,000.0 |  |  |  |  |  |  |
Employee Stock Plan, 2008 Plan |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  |  | 6,000,000.0 |  |  |  |  |  |  |
Maximum number of shares per employee (in shares) |  |  | 400,000 |  |  |  |  |  |  |
Option Plans 2008 | Minimum |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Percentage of option price for fair value of ordinary share (percentage) |  |  | 100.00% |  |  |  |  |  |  |
Employee Stock Plan, 2003 Plan |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  |  |  |  | 6,000,000.0 |  |  |  |  |
Maximum number of shares per employee (in shares) |  |  |  |  | 400,000 |  |  |  |  |
Maximum number of award as percentage of shares outstanding (percentage) |  |  |  |  | 10.00% |  |  |  |  |
Employee Stock Option |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Weighted average contractual term of options outstanding | 4 years 10 months 24 days | 4 years 10 months 9 days |  |  |  |  |  |  |  |
Weighted average fair value per option (USD per share) |  |  |  |  |  | $ 25.97 |  |  |  |
Exercisable - number of shares (in shares) | 336,942 |  |  |  |  | 336,942 |  |  |  |
Exercisable - weighted average remaining contractual life | 3 years 7 months 17 days |  |  |  |  |  |  |  |  |
Exercisable - weighted average exercise price (USD per share) | $ 92.71 |  |  |  |  | $ 92.71 |  |  |  |
Fully vested total intrinsic value | $ 38,400,000 |  |  |  |  | $ 38,400,000 |  |  |  |
Intrinsic value of option exercised |  |  |  |  |  | $ 700,000 | $ 4,300,000 |  |  |
Employee Stock Option | Award Date, All years excluding 2018 |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Shares vesting period |  |  |  |  |  | 5 years |  |  |  |
Shares expiration period |  |  |  |  |  | 8 years |  |  |  |
Employee Stock Option | Non-executive directors | Award Date, 2018 |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Shares vesting period |  |  |  |  |  | 12 months |  |  |  |
Shares expiration period |  |  |  |  |  | 8 years |  |  |  |
Employee Stock Option | Minimum |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Options outstanding fair value (USD per share) | $ 12.24 |  |  |  |  | $ 12.24 |  |  |  |
Employee Stock Option | Maximum |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Weighted average contractual term of options outstanding | 8 years |  |  |  |  |  |  |  |  |
Options outstanding fair value (USD per share) | $ 64.07 |  |  |  |  | $ 64.07 |  |  |  |
Restricted Stock Units 2013 |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  |  |  | 4,100,000 |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  |  |  | 2,500,000 |  |  |  |  |  |
Consultants Restricted Stock Units 2019 |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Ordinary shares which have been reserved for issuance (in shares) |  |  |  |  |  |  |  |  | 250,000 |
Consultants Restricted Stock Units 2019 | Non-executive directors |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Shares vesting period |  |  |  |  |  | 12 months |  |  |  |
Performance Share Unit (PSUs) |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Fair value of stock units vested |  |  |  |  |  | $ 5,100,000 |  | $ 5,300,000 |  |
Restricted Stock Units (RSUs) |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Fair value of stock units vested |  |  |  |  |  | $ 16,100,000 |  | $ 14,300,000 |  |
PSUs Based on Service and EPS Targets | Maximum |  |  |  |  |  |  |  |  |  |
Compensation Related Costs Share Based Payments Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |
Stock units to be granted (in shares) | 83,897 |  |  |  |  | 83,897 |  |  |  |

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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + 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 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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