Segmented Information (Schedule of Revenue and (Loss) Income Before Taxes by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting [Line Items]
Revenue	$ 332,194	$ 289,796	$ 393,222	$ 303,429	$ 355,972	$ 245,346	$ 308,530	$ 260,178	$ 291,750	$ 227,401	$ 252,613	$ 199,427	$ 1,318,641	$ 1,170,026	$ 971,191
SG&A expenses													382,389	382,676	323,270
Impairment loss													0	0	8,911
Acquisition-related costs													777	5,093	38,272
D&A expenses													70,501	66,614	52,694
Gain on disposition of property, plant and equipment ("PPE")													(1,107)	(2,731)	(1,656)
Foreign exchange (gain) loss													(2,937)	(212)	2,559
Operating income	71,484	40,160	77,970	33,588	56,327	31,194	64,795	32,873	40,038	16,931	26,888	23,597	223,202	185,189	107,454
Interest expense													(41,277)	(44,527)	(38,291)
Other income, net													8,838	11,850	8,231
Income tax expense													(41,623)	(31,006)	(2,088)
Net income	$ 51,565	$ 25,272	$ 54,131	$ 18,172	$ 35,460	$ 23,112	$ 45,727	$ 17,207	$ 36,837	$ 10,323	$ 17,713	$ 10,433	149,140	121,506	75,306
Operating Segments [Member]
Segment Reporting [Line Items]
Revenue													1,318,641	1,170,026	971,191
SG&A expenses													382,389	382,676	323,270
Impairment loss															8,911
Segment profit													290,436	253,953	199,323
Acquisition-related costs													777	5,093	38,272
D&A expenses													70,501	66,614	52,694
Gain on disposition of property, plant and equipment ("PPE")													(1,107)	(2,731)	(1,656)
Foreign exchange (gain) loss													(2,937)	(212)	2,559
Operating income													223,202	185,189	107,454
Interest expense													(41,277)	(44,527)	(38,291)
Other income, net													8,838	11,850	8,231
Income tax expense													(41,623)	(31,006)	(2,088)
Net income													149,140	121,506	75,306
Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue													1,193,440	1,046,518	870,797
SG&A expenses													358,016	363,549	308,873
Impairment loss															8,911
Segment profit													254,764	221,200	170,830
Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue													125,201	123,508	100,394
SG&A expenses													24,373	19,127	14,397
Segment profit													35,672	32,753	28,493
Service Revenue [Member]
Segment Reporting [Line Items]
Revenue													804,024	749,515	624,417
Direct expenses													164,977	159,058	133,189
Service Revenue [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue													804,024	749,515	624,417
Direct expenses													164,977	159,058	133,189
Service Revenue [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue													678,823	626,007	524,023
Direct expenses													99,821	87,430	75,685
Service Revenue [Member] | Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue													125,201	123,508	100,394
Direct expenses													65,156	71,628	57,504
Inventory Sales Revenue [Member]
Segment Reporting [Line Items]
Revenue													514,617	420,511	346,774
Direct expenses													480,839	374,339	306,498
Inventory Sales Revenue [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue													514,617	420,511	346,774
Direct expenses													480,839	374,339	306,498
Inventory Sales Revenue [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenue													514,617	420,511	346,774
Direct expenses													$ 480,839	$ 374,339	$ 306,498