Segmented Information (Schedule of Revenue and (Loss) Income Before Taxes by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Line Items]
Revenues	$ 355,972	$ 245,346	$ 308,530	$ 260,178	$ 291,750	$ 227,401	$ 252,613	$ 199,427	$ 294,830	$ 300,976	$ 275,667	$ 255,504	$ 1,170,026	$ 971,191	$ 1,126,977
SG&A expenses													382,676	323,270	283,529
Impairment loss														8,911	28,243
Gross revenue, net of expenses															188,561
Acquisition-related costs													5,093	38,272	11,829
Depreciation and amortization expenses ("D&A")													66,614	52,694	40,861
Gain on disposition of property, plant and equipment ("PPE")													(2,731)	(1,656)	(1,282)
Unrealized foreign exchange loss													(212)	2,559	1,431
Operating income	56,327	31,194	64,795	32,873	40,038	16,931	26,888	23,597	40,628	2,285	53,635	39,174	185,189	107,454	135,722
Interest expense													(44,527)	(38,291)	(5,564)
Debt extinguishment costs															(6,787)
Other income, net													11,850	8,231	7,123
Income tax expense													(31,006)	(2,088)	(36,982)
Net income	$ 35,460	$ 23,112	$ 45,727	$ 17,207	$ 36,837	$ 10,323	$ 17,713	$ 10,433	$ 27,927	$ (5,000)	$ 40,591	$ 29,994	121,506	75,306	93,512
Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													1,170,026	971,191	1,126,977
SG&A expenses													382,676	323,270
Impairment loss														8,911
Gross revenue, net of expenses													253,953	199,323
Acquisition-related costs														38,272
Depreciation and amortization expenses ("D&A")													66,614	52,694
Gain on disposition of property, plant and equipment ("PPE")														(1,656)
Unrealized foreign exchange loss														(2,559)
Operating income													185,189	107,454
Interest expense													(44,527)	(38,291)
Other income, net													11,850	8,231
Income tax expense													(31,006)	(2,088)
Net income													121,506	75,306
Segment Reconciling Items [Member]
Segment Reporting [Line Items]
Acquisition-related costs													5,093		11,829
Depreciation and amortization expenses ("D&A")															40,861
Gain on disposition of property, plant and equipment ("PPE")													(2,731)		(1,282)
Unrealized foreign exchange loss													(212)		(1,431)
Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													1,046,518	870,797	1,045,174
SG&A expenses													363,549	308,873	272,317
Impairment loss														8,911	28,243
Gross revenue, net of expenses													221,200	170,830	166,018
Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													123,508	100,394	81,803
SG&A expenses													19,127	14,397	11,212
Gross revenue, net of expenses													32,753	28,493	22,543
Service Revenues [Member]
Segment Reporting [Line Items]
Revenues													749,515	624,417	555,843
Direct expenses													159,058	133,189	113,296
Service Revenues [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													749,515	624,417	555,843
Direct expenses													159,058	133,189
Service Revenues [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													626,007	524,023	474,040
Direct expenses													87,430	75,685	65,248
Service Revenues [Member] | Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													123,508	100,394	81,803
Direct expenses													71,628	57,504	48,048
Revenue from Inventory Sales [Member]
Segment Reporting [Line Items]
Revenues													420,511	346,774	571,134
Direct expenses													374,339	306,498	513,348
Revenue from Inventory Sales [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													420,511	346,774	571,134
Direct expenses													374,339	306,498
Revenue from Inventory Sales [Member] | Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													420,511	346,774	571,134
Direct expenses													$ 374,339	$ 306,498	$ 513,348