Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net income	$ 121,506,000	$ 75,306,000	$ 93,512,000
Adjustments for items not affecting cash:
Depreciation and amortization expenses	66,614,000	52,694,000	40,861,000
Impairment loss		8,911,000	28,243,000
Stock option compensation expense	8,252,000	13,700,000	5,507,000
Equity-classified PSU expense	11,256,000	3,529,000	1,981,000
Deferred income tax expense (recovery)	6,239,000	(17,268,000)	(3,359,000)
Unrealized foreign exchange loss	951,000	254,000	1,947,000
Gain on disposition of property, plant and equipment	(2,731,000)	(1,656,000)	(1,282,000)
Amortization of debt issuance costs	4,995,000	3,056,000	359,000
Gain on disposition of equity investment	(4,935,000)
Other, net	(2,317,000)	(1,237,000)	(893,000)
Net changes in operating assets and liabilities	(65,550,000)	10,279,000	10,682,000
Net cash provided by operating activities	144,280,000	147,568,000	177,558,000
Investing activities:
Acquisition of contingently redeemable NCI			(41,092,000)
Acquisition of NCI			(226,000)
Property, plant and equipment additions	(16,860,000)	(10,812,000)	(18,918,000)
Intangible asset additions	(26,152,000)	(28,584,000)	(17,558,000)
Proceeds on disposition of property, plant and equipment	10,586,000	4,985,000	6,691,000
Proceeds on disposal of equity investment	6,147,000
Other, net	(4,674,000)	(692,000)	(248,000)
Net cash used in investing activities	(30,953,000)	(710,954,000)	(116,862,000)
Financing activities:
Dividends paid to stockholders	(75,678,000)	(72,785,000)	(70,459,000)
Dividends paid to NCI		(41,000)	(3,436,000)
Issuances of share capital	28,524,000	9,936,000	24,338,000
Share repurchase			(36,726,000)
Payment of withholding taxes on issuance of shares	(3,901,000)
Proceeds from short-term debt	19,715,000	6,971,000	67,584,000
Repayment of short-term debt	(6,628,000)	(24,479,000)	(57,516,000)
Proceeds from long-term debt		325,000,000	647,091,000
Repayment of long-term debt	(91,013,000)	(108,985,000)	(148,158,000)
Debt issue costs		(12,624,000)	(10,644,000)
Debt extinguishment costs			(6,787,000)
Repayment of finance lease obligations	(3,950,000)	(2,322,000)	(1,655,000)
Other, net	(1,176,000)	(1,408,000)	511,000
Net cash provided by (used in) financing activities	(134,107,000)	119,263,000	404,143,000
Effect of changes in foreign currency rates on cash, cash equivalents, and restricted cash	(4,769,000)	17,150,000	4,000
Increase (decrease)	(25,549,000)	(426,973,000)	464,843,000
Beginning of period	331,116,000	758,089,000	293,246,000
Cash, cash equivalents, and restricted cash, end of period	$ 305,567,000	331,116,000	758,089,000
Iron Planet Holdings Inc. [Member]
Investing activities:
Acquisition, net of cash acquired		$ (675,851,000)
Mascus International Holdings BV [Member]
Investing activities:
Acquisition, net of cash acquired			(28,123,000)
Petrowsky Auctioneers Inc. [Member]
Investing activities:
Acquisition of equity investments			(6,250,000)
Kramer Auctions Ltd. [Member]
Investing activities:
Acquisition of equity investments			$ (11,138,000)