Segmented information (Schedule of Revenue and Net income by Segment) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting [Line Items]
Revenue	$ 393,921,000	$ 331,555,000
Selling, general and administrative expenses ("SG&A")	126,606,000	114,239,000
Acquisition-related costs	9,637,000	2,922,000
Depreciation and amortization expenses ("D&A")	24,225,000	21,070,000
Gain on disposition of property, plant and equipment ("PPE")	(169,820,000)	(68,000)
Foreign exchange loss	(164,000)	277,000
Total operating expenses	330,901,000	287,121,000
Operating income	232,840,000	44,502,000
Interest expense	(20,686,000)	(8,946,000)
Change in fair value of derivatives, net	1,263,000
Other income, net	920,000	1,002,000
Income tax expense	(36,236,000)	(8,419,000)
Net income	178,101,000	28,139,000
Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	393,921,000	331,555,000
Selling, general and administrative expenses ("SG&A")	126,606,000	114,239,000
Segment profit	96,718,000	68,703,000
Acquisition-related costs	9,637,000	2,922,000
Depreciation and amortization expenses ("D&A")	24,225,000	21,070,000
Gain on disposition of property, plant and equipment ("PPE")	169,820,000	68,000
Foreign exchange loss	(164,000)	277,000
Total operating expenses	330,901,000	287,121,000
Operating income	232,840,000	44,502,000
Interest expense	(20,686,000)	(8,946,000)
Change in fair value of derivatives, net	1,263,000
Other income, net	920,000	1,002,000
Income tax expense	(36,236,000)	(8,419,000)
Net income	178,101,000	28,139,000
Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	350,064,000	297,596,000
Selling, general and administrative expenses ("SG&A")	108,811,000	102,781,000
Segment profit	84,097,000	59,764,000
Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	43,857,000	33,959,000
Selling, general and administrative expenses ("SG&A")	17,795,000	11,458,000
Segment profit	12,621,000	8,939,000
Commissions
Segment Reporting [Line Items]
Revenue	116,375,000	103,975,000
Commissions | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	116,375,000	103,975,000
Commissions | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	116,375,000	103,975,000
Fees
Segment Reporting [Line Items]
Revenue	128,486,000	102,055,000
Fees | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	128,486,000	102,055,000
Fees | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	84,629,000	68,096,000
Fees | Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	43,857,000	33,959,000
Service Revenues [Member]
Segment Reporting [Line Items]
Revenue	244,861,000	206,030,000
Direct expenses	39,015,000	37,866,000
Service Revenues [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	244,861,000	206,030,000
Direct expenses	39,015,000	37,866,000
Service Revenues [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	201,004,000	172,071,000
Direct expenses	25,574,000	24,304,000
Service Revenues [Member] | Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	43,857,000	33,959,000
Direct expenses	13,441,000	13,562,000
Inventory Sales Revenue [Member]
Segment Reporting [Line Items]
Revenue	149,060,000	125,525,000
Direct expenses	131,582,000	110,747,000
Inventory Sales Revenue [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	149,060,000	125,525,000
Direct expenses	131,582,000	110,747,000
Inventory Sales Revenue [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue	149,060,000	125,525,000
Direct expenses	$ 131,582,000	$ 110,747,000