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Share capital (Details) - Buyback Program - USD ($) $ in Millions		6 Months Ended	12 Months Ended
	Dec. 31, 2019	Jun. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 08, 2019
Equity, Class of Treasury Stock [Line Items]
Share repurchase program, number of shares authorized to be repurchased (in shares)					1,000,000.0
Shares redeemed, value	$ 5.3		$ 175.0	$ 141.6
Shares redeemed (in shares)	35,100	0	1,235,218
Maximum
Equity, Class of Treasury Stock [Line Items]
Share repurchase program, authorized percentage		10.00%

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The number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

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Number of shares that have been repurchased and retired during the period.

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Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

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