Segmented Information (Schedule of Revenue and (Loss) Income Before Taxes by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting [Line Items]
Revenues	$ 128,876	$ 109,318	$ 419,626	$ 380,413
Costs of services, excluding depreciation and amortization	(14,750)	(12,045)	(49,821)	(40,681)
Selling, general and administrative expenses	(69,000)	(58,170)	(211,153)	(187,165)
Depreciation and amortization expenses	(10,196)	(10,017)	(30,560)	(31,402)
Impairment loss	(28,243)		(28,243)
Acquisition-related costs	(4,691)		(5,440)
Gain on disposition of property, plant and equipment	570	234	1,017	1,200
Foreign exchange gain (loss)	(281)	(718)	(332)	2,051
Operating income	2,285	28,602	95,094	124,416
Equity income	213	363	1,209	769
Other and income tax expense	(7,498)	(7,718)	(30,718)	(33,982)
Net income (loss)	(5,000)	21,247	65,585	91,203
Operating Segments [Member]
Segment Reporting [Line Items]
Revenues	128,876	109,318	419,626	380,413
Costs of services, excluding depreciation and amortization	(14,750)	(12,045)	(49,821)	(40,681)
Selling, general and administrative expenses	(69,000)	(58,170)	(211,153)	(187,165)
Depreciation and amortization expenses	(10,196)	(10,017)	(30,560)	(31,402)
Impairment loss	(28,243)		(28,243)
Operating income	6,687	29,086	99,849	121,165
Segment Reconciling Items [Member]
Segment Reporting [Line Items]
Gain on disposition of property, plant and equipment	570	234	1,017	1,200
Foreign exchange gain (loss)	(281)	(718)	(332)	2,051
Core Auction [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues	122,789	105,421	402,671	369,711
Costs of services, excluding depreciation and amortization	(14,131)	(12,045)	(48,354)	(40,681)
Selling, general and administrative expenses	(63,998)	(54,797)	(197,222)	(177,196)
Depreciation and amortization expenses	(9,259)	(9,357)	(27,960)	(29,025)
Operating income	35,401	29,222	129,135	122,809
Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues	6,087	3,897	16,955	10,702
Costs of services, excluding depreciation and amortization	(619)		(1,467)
Selling, general and administrative expenses	(5,002)	(3,373)	(13,931)	(9,969)
Depreciation and amortization expenses	(937)	(660)	(2,600)	(2,377)
Impairment loss	(28,243)		(28,243)
Operating income	$ (28,714)	$ (136)	$ (29,286)	$ (1,644)