Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Number of options outstanding, including both vested and non-vested options.

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Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Stock options - Plans (Details) - shares	1 Months Ended		3 Months Ended
Stock options - Plans (Details) - shares	Jan. 31, 2020	Jun. 30, 2017	Mar. 31, 2020	Dec. 31, 2019
Share-based awards
Number of shares outstanding			6,049,288	4,720,772
2017 Plan
Share-based awards
Number of shares authorized		2,255,000
Cumulative annual increase in number of shares issuable (as a percent)		4.00%
Number of shares available for future issuance			1,642,679
Additional shares authorized	1,815,520
Vesting period (in years)			4 years
2017 Plan \| Maximum
Share-based awards
Expiration period			10 years