Segmented information (Schedule of Revenue and Net income by Segment) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting [Line Items]
Revenue	$ 331,555,000	$ 273,255,000
Selling, general and administrative expenses ("SG&A")	116,078,000	98,385,000
Acquisition-related costs	2,922,000
Depreciation and amortization expenses ("D&A")	21,070,000	19,293,000
Gain on disposition of property, plant and equipment ("PPE")	(68,000)	(47,000)
Foreign exchange loss	277,000	602,000
Operating income	44,502,000	34,082,000
Interest expense	(8,946,000)	(9,182,000)
Other income, net	1,002,000	3,577,000
Income tax expense	(8,419,000)	(5,648,000)
Net income	28,139,000	22,829,000
Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	331,555,000	273,255,000
Selling, general and administrative expenses ("SG&A")	116,078,000	98,385,000
Segment profit	68,703,000	53,930,000
Acquisition-related costs	2,922,000
Depreciation and amortization expenses ("D&A")	21,070,000	19,293,000
Gain on disposition of property, plant and equipment ("PPE")	(68,000)	(47,000)
Foreign exchange loss	277,000	602,000
Operating income	44,502,000	34,082,000
Interest expense	(8,946,000)	(9,182,000)
Other income, net	1,002,000	3,577,000
Income tax expense	(8,419,000)	(5,648,000)
Net income	28,139,000	22,829,000
Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	296,280,000	244,875,000
Selling, general and administrative expenses ("SG&A")	104,345,000	91,585,000
Segment profit	59,598,000	46,610,000
Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	35,275,000	28,380,000
Selling, general and administrative expenses ("SG&A")	11,733,000	6,800,000
Segment profit	9,105,000	7,320,000
Service Revenue [Member]
Segment Reporting [Line Items]
Revenue	206,030,000	183,123,000
Direct expenses	36,027,000	39,355,000
Service Revenue [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	206,030,000	183,123,000
Direct expenses	36,027,000	39,355,000
Service Revenue [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	170,755,000	154,743,000
Direct expenses	21,590,000	25,095,000
Service Revenue [Member] | Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	35,275,000	28,380,000
Direct expenses	14,437,000	14,260,000
Inventory Sales Revenue [Member]
Segment Reporting [Line Items]
Revenue	125,525,000	90,132,000
Direct expenses	110,747,000	81,585,000
Inventory Sales Revenue [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	125,525,000	90,132,000
Direct expenses	110,747,000	81,585,000
Inventory Sales Revenue [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	125,525,000	90,132,000
Direct expenses	$ 110,747,000	$ 81,585,000