Segmented information (Schedule of Carrying Value Goodwill) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill	$ 672,310	$ 671,594	$ 670,922
Auctions and Marketplaces [Member]
Goodwill	652,243	651,359
Auctions and Marketplaces [Member] | Mascus International Holdings BV [Member]
Goodwill	652,243
Other Reporting Unit [Member]
Goodwill	20,067	$ 20,235
Other Reporting Unit [Member] | Mascus International Holdings BV [Member]
Goodwill	$ 20,067