Segmented Information (Schedule of Revenue and (Loss) Income Before Taxes by Segment) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting [Line Items]
Revenues	$ 166,186	$ 158,805	$ 290,685	$ 290,750
Costs of services, excluding depreciation and amortization	(21,591)	(19,758)	(34,404)	(35,071)
SG&A expenses	(74,377)	(73,992)	(144,952)	(141,102)
Depreciation and amortization expenses	(11,872)	(10,284)	(22,210)	(20,364)
Impairment loss	(8,911)		(8,911)
Acquisition-related costs	(22,948)	(603)	(31,575)	(1,800)
Gain on disposition of property, plant and equipment	308	201	1,029	447
Foreign exchange gain (loss)	93	(734)	823	(51)
Operating income	26,888	53,635	50,485	92,809
Equity income (loss)	4	477	(49)	996
Other and income tax expense	(9,179)	(13,521)	(22,290)	(23,220)
Net income	17,713	40,591	28,146	70,585
Operating Segments [Member]
Segment Reporting [Line Items]
Revenues	166,186	158,805	290,685	290,750
Costs of services, excluding depreciation and amortization	(21,591)	(19,758)	(34,404)	(35,071)
SG&A expenses	(74,377)	(73,992)	(144,952)	(141,102)
Depreciation and amortization expenses	(11,872)	(10,284)	(22,210)	(20,364)
Impairment loss	(8,911)		(8,911)
Operating income	49,435	54,771	80,208	94,213
Segment Reconciling Items [Member]
Segment Reporting [Line Items]
Acquisition-related costs	(22,948)	(603)	(31,575)	(1,800)
Gain on disposition of property, plant and equipment	308	201	1,029	447
Foreign exchange gain (loss)	93	(734)	823	(51)
Core Auction [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues	148,028	152,542	265,800	279,882
Costs of services, excluding depreciation and amortization	(17,981)	(19,438)	(30,019)	(34,223)
SG&A expenses	(64,763)	(68,848)	(130,333)	(133,362)
Depreciation and amortization expenses	(9,440)	(9,397)	(18,894)	(18,701)
Impairment loss	(3,444)		(3,444)
Operating income	52,400	54,859	83,110	93,596
Other Reporting Unit [Member] | Operating Segments [Member]
Segment Reporting [Line Items]
Revenues	18,158	6,263	24,885	10,868
Costs of services, excluding depreciation and amortization	(3,610)	(320)	(4,385)	(848)
SG&A expenses	(9,614)	(5,144)	(14,619)	(7,740)
Depreciation and amortization expenses	(2,432)	(887)	(3,316)	(1,663)
Impairment loss	(5,467)		(5,467)
Operating income	$ (2,965)	$ (88)	$ (2,902)	$ 617