Segmented Information (Schedule of Revenue and (Loss) Income Before Taxes by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting [Line Items]
Revenues	$ 124,499	$ 131,945
Costs of services, excluding depreciation and amortization	(12,813)	(15,313)
SG&A expenses	(70,575)	(67,110)
Depreciation and amortization expenses	(10,338)	(10,080)
Acquisition-related costs	(8,627)	(1,197)
Gain on disposition of property, plant and equipment	721	246
Foreign exchange gain	730	683
Operating income	23,597	39,174
Equity income (loss)	(53)	519
Other and income tax expense	(13,111)	(9,699)
Net income	10,433	29,994
Operating Segments [Member]
Segment Reporting [Line Items]
Revenues	124,499	131,945
Costs of services, excluding depreciation and amortization	(12,813)	(15,313)
SG&A expenses	(70,575)	(67,110)
Depreciation and amortization expenses	(10,338)	(10,080)
Operating income	30,773	39,442
Segment Reconciling Items [Member]
Segment Reporting [Line Items]
Acquisition-related costs	(8,627)	(1,197)
Gain on disposition of property, plant and equipment	721	246
Foreign exchange gain	730	683
Core Auction [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues	117,772	127,340
Costs of services, excluding depreciation and amortization	(12,038)	(14,785)
SG&A expenses	(65,570)	(64,514)
Depreciation and amortization expenses	(9,454)	(9,304)
Operating income	30,710	38,737
Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues	6,727	4,605
Costs of services, excluding depreciation and amortization	(775)	(528)
SG&A expenses	(5,005)	(2,596)
Depreciation and amortization expenses	(884)	(776)
Operating income	$ 63	$ 705