Segmented Information (Schedule of Revenue and (Loss) Income Before Taxes by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Line Items]
Revenues	$ 178,785	$ 141,047	$ 166,186	$ 124,499	$ 146,769	$ 128,876	$ 158,805	$ 131,945	$ 135,462	$ 109,318	$ 155,477	$ 115,618	$ 610,517	$ 566,395	$ 515,875
Costs of services, excluding D&A													(79,013)	(66,062)	(56,026)
SG&A expenses													(323,270)	(283,529)	(254,389)
Impairment loss													(8,911)	(28,243)
Acquisition-related costs													(38,272)	(11,829)	(601)
Depreciation and amortization expenses													(52,694)	(40,861)	(42,032)
Gain on disposition of property, plant and equipment													1,656	1,282	9,691
Foreign exchange gain (loss)													(2,559)	(1,431)	2,322
Operating income	40,038	16,931	26,888	23,597	40,628	2,285	53,635	39,174	50,424	28,602	62,795	33,019	107,454	135,722	174,840
Other income (expense)													(30,060)	(5,228)	1,596
Income tax recovery (expense)													2,088	36,982	37,861
Net income	36,837	10,323	17,713	10,433	$ 27,927	$ (5,000)	$ 40,591	$ 29,994	$ 47,372	$ 21,247	$ 45,846	$ 24,110	75,306	93,512	138,575
Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													610,517	566,395	515,875
Costs of services, excluding D&A													(79,013)	(66,062)	(56,026)
SG&A expenses													(323,270)	(283,529)	(254,389)
Impairment loss													(8,911)	(28,243)
Operating income													199,323	188,561	205,460
Segment Reconciling Items [Member]
Segment Reporting [Line Items]
Acquisition-related costs													(38,272)	(11,829)	(601)
Depreciation and amortization expenses													(52,694)	(40,861)	(42,032)
Gain on disposition of property, plant and equipment													1,656	1,282	9,691
Foreign exchange gain (loss)													(2,559)	(1,431)	2,322
Auctions and Marketplaces [Member]
Segment Reporting [Line Items]
SG&A expenses	(272,317)	(81,736)	(70,977)	(67,111)
Auctions and Marketplaces [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													564,298	531,826	505,865
Costs of services, excluding D&A													(75,685)	(65,248)	(56,026)
SG&A expenses													(308,874)	(272,317)	(249,852)
Impairment loss													(8,911)	(28,243)
Operating income													170,828	166,018	199,987
Other Reporting Unit [Member]
Segment Reporting [Line Items]
SG&A expenses	$ (11,212)	$ (3,599)	$ (3,400)	$ (3,464)
Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues													46,219	34,569	10,010
Costs of services, excluding D&A													(3,328)	(814)
SG&A expenses													(14,396)	(11,212)	(4,537)
Operating income													$ 28,495	$ 22,543	$ 5,473