Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Common stock [Member]	Additional paid-in capital ("APIC") [Member]	Retained earnings [Member]	Accumulated other comprehensive income (loss) [Member]	Non-controlling interest ("NCI") [Member]	Contingently redeemable non-controlling interest [Member]	Performance Share Units [Member]	Total
Balance at Dec. 31, 2014	$ 141,257	$ 31,314	$ 536,111	$ (16,750)				$ 691,932
Balance, shares at Dec. 31, 2014	107,687,935
Net income			136,214		$ 64			136,278
Other comprehensive income (loss)				(40,383)				(40,383)
Comprehensive income			136,214	(40,383)	64			95,895
Change in value of contingently redeemable NCI			(6,934)					(6,934)
Stock option exercises	$ 37,762	(7,946)						29,816
Stock option exercises, shares	1,412,535
Stock option tax adjustment		359						359
Stock option compensation expense (note 28)		4,001						4,001
NCI acquired in a business combination (note 32)					4,119			4,119
Shares repurchased (note 27)	$ (47,489)							(47,489)
Shares repurchased (note 27), shares	(1,900,000)
Cash dividends paid (note 27)			(64,340)					(64,340)
Balance at Dec. 31, 2015	$ 131,530	27,728	601,051	(57,133)	4,183			707,359
Balance, shares at Dec. 31, 2015	107,200,470
Contingently redeemable non-controlling interest, Balance at Dec. 31, 2014						$ 17,287
Net income						2,297
Other comprehensive income (loss)						(393)
Comprehensive Income attributable redeemable non-controlling interests						1,904
Change in value of contingently redeemable NCI						6,934
Cash dividends paid (note 27)						(1,340)
Contingently redeemable non-controlling interest, Balance at Dec. 31, 2015						24,785
Net income			91,832		346			92,178
Other comprehensive income (loss)				(9,993)	(23)			(10,016)
Comprehensive income			91,832	(9,993)	323			82,162
Change in value of contingently redeemable NCI			(21,186)					(21,186)
Stock option exercises	$ 30,670	(6,332)						24,338
Stock option exercises, shares	1,081,531
Stock option tax adjustment		443						443
Stock option compensation expense (note 28)		5,507						5,507
Modification of PSUs (note 28)			(70)				$ 2,175	(70)
Equity-classified PSU expense (note 28)		283					1,698	283
Equity-classified PSU dividend equivalents		9	(62)				42	(53)
Change in value of contingently redeemable equity-classified PSUs			(35)				35	(35)
NCI acquired in a business combination (note 32)					596			596
Acquisition of NCI					(226)			(226)
Shares repurchased (note 27)	$ (36,726)							$ (36,726)
Shares repurchased (note 27), shares	(1,460,000)							(1,460,000)
Cash dividends paid (note 27)			(70,459)					$ (70,562)
Cash dividends paid (note 27)					(103)	(44,141)
Balance at Dec. 31, 2016	$ 125,474	27,638	601,071	(67,126)	4,773			691,830
Balance, shares at Dec. 31, 2016	106,822,001
Contingently redeemable Performance share units, Balance at Dec. 31, 2016							3,950	3,950
Net income						1,334
Other comprehensive income (loss)						169
Comprehensive Income attributable redeemable non-controlling interests						1,503
Change in value of contingently redeemable NCI						21,186
Cash dividends paid (note 27)						$ (3,333)
Net income			75,027		279			75,306
Other comprehensive income (loss)				24,612	58			24,670
Comprehensive income			75,027	24,612	337			99,976
Stock option exercises	$ 13,017	(3,081)						9,936
Stock option exercises, shares	444,571
Stock option compensation expense (note 28)		13,700						13,700
Assumption of stock options on acquisition of IronPlanet (note 22)		2,330						2,330
Settlement of equity-classified PSUs	$ 91						(172)	91
Settlement of equity-classified PSUs, shares	3,211
Modification of PSUs (note 28)			(382)				1,803	(382)
Equity-classified PSU expense (note 28)		340					3,189	340
Equity-classified PSU dividend equivalents		78	(227)				149	(149)
Change in value of contingently redeemable equity-classified PSUs			(95)				95	$ (95)
Shares repurchased (note 27), shares								0
Cash dividends paid (note 27)			(72,785)					$ (72,826)
Cash dividends paid (note 27)					(41)
Balance at Dec. 31, 2017	$ 138,582	$ 41,005	$ 602,609	$ (42,514)	$ 5,069			744,751
Balance, shares at Dec. 31, 2017	107,269,783
Contingently redeemable Performance share units, Balance at Dec. 31, 2017							$ 9,014	$ 9,014