Segmented information (Schedule of Revenue and Net income by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting [Line Items]
Revenue	$ 273,255	$ 303,429
Selling, general and administrative expenses ("SG&A")	98,385	95,184
Acquisition-related costs		669
Depreciation and amortization expenses ("D&A")	19,293	17,115
Gain on disposition of property, plant and equipment ("PPE")	(47)	(149)
Foreign exchange loss	602	478
Operating income	34,082	33,588
Interest expense	(9,182)	(10,816)
Other income, net	3,577	2,039
Income tax expense	(5,648)	(6,639)
Net income	22,829	18,172
Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	273,255	303,429
Selling, general and administrative expenses ("SG&A")	98,385	95,184
Segment profit	53,930	51,701
Acquisition-related costs		669
Depreciation and amortization expenses ("D&A")	19,293	17,115
Gain on disposition of property, plant and equipment ("PPE")	(47)	(149)
Foreign exchange loss	602	478
Operating income	34,082	33,588
Interest expense	(9,182)	(10,816)
Other income, net	3,577	2,039
Income tax expense	(5,648)	(6,639)
Net income	22,829	18,172
Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	244,875	274,494
Selling, general and administrative expenses ("SG&A")	91,585	89,182
Segment profit	46,610	44,020
Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	28,380	28,935
Selling, general and administrative expenses ("SG&A")	6,800	6,002
Segment profit	7,320	7,681
Service Revenue [Member]
Segment Reporting [Line Items]
Revenue	183,123	172,372
Direct expenses	39,355	36,069
Service Revenue [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	183,123	172,372
Direct expenses	39,355	36,069
Service Revenue [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	154,743	143,437
Direct expenses	25,095	20,817
Service Revenue [Member] | Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	28,380	28,935
Direct expenses	14,260	15,252
Inventory Sales Revenue [Member]
Segment Reporting [Line Items]
Revenue	90,132	131,057
Direct expenses	81,585	120,475
Inventory Sales Revenue [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	90,132	131,057
Direct expenses	81,585	120,475
Inventory Sales Revenue [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	90,132	131,057
Direct expenses	$ 81,585	$ 120,475