Shareholders' equity (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Oct. 24, 2018
Stockholders' Equity Note [Abstract]
Share repurchase program, authorized amount						$ 500,000
Common shares repurchased (in shares)	0	499	718	499	1,757
Payments for common shares repurchased		$ 14,000		$ 14,000	$ 78,896
Amount remaining under share repurchase authorization	$ 287,452			$ 287,452

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Balance Type:	na
Period Type:	duration