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 Performance Share Units [Member]	Total
Balance at Dec. 31, 2016	$ 125,474	$ 27,638	$ 601,071	$ (67,126)	$ 4,773	$ 3,950	$ 691,830
Balance, shares at Dec. 31, 2016	106,822,001
Net income			75,027		279		75,306
Other comprehensive income (loss)				24,612	58
Other comprehensive income (loss)							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		13,700					13,700
Assumption of stock options on acquisition of IronPlanet		2,330					2,330
Settlement of equity-classified PSUs	$ 91					(172)	91
Settlement of equity-classified PSUs, shares	3,211
Modification of PSUs			(382)			1,803	(382)
Equity-classified PSU expense		340				3,189	340
Equity-classified share units dividend equivalents		78	(227)			149	(149)
Change in value of contingently redeemable equity-classified PSUs			(95)			95	(95)
Cash dividends paid			(72,785)		(41)		(72,826)
Balance at Dec. 31, 2017	$ 138,582	41,005	602,609	(42,514)	5,069	9,014	744,751
Balance, shares at Dec. 31, 2017	107,269,783
Net income			121,479		27		121,506
Other comprehensive income (loss)				(13,763)	(29)
Other comprehensive income (loss)							(13,792)
Comprehensive income			121,479	(13,763)	(2)		107,714
Stock option exercises	$ 37,308	(8,784)					28,524
Stock option exercises, shares	1,235,154
Issuance of common stock related to vesting of share units	$ 5,890	(1,662)	(326)			(7,803)	3,902
Issuance of common stock related to vesting of share units, shares	177,093
Stock option compensation expense		8,252					8,252
Modification of PSUs		12,365	958			(6,622)	13,323
Equity-classified PSU expense		5,384				5,872	5,384
Equity-classified share units dividend equivalents		325	(678)			353	(353)
Change in value of contingently redeemable equity-classified PSUs			(109)			109	(109)
Cash dividends paid			(75,678)				(75,678)
Balance at Dec. 31, 2018	$ 181,780	56,885	648,255	(56,277)	5,067	923	835,710
Balance, shares at Dec. 31, 2018	108,682,030
Net income			149,039		101		149,140
Other comprehensive income (loss)				(2,822)	(14)
Other comprehensive income (loss)							(2,836)
Comprehensive income			149,039	(2,822)	87		146,304
Stock option exercises	$ 49,117	(8,023)					41,094
Stock option exercises, shares	1,672,022
Issuance of common stock related to vesting of share units	$ 5,886	(10,064)	1			(1,083)	(4,177)
Issuance of common stock related to vesting of share units, shares	207,403
Stock option compensation expense		4,697					4,697
Equity-classified PSU expense		7,933				114	7,933
Equity-classified share units dividend equivalents		682	(709)			$ 46	(27)
Cash dividends paid			(82,535)				(82,535)
Shares repurchased	$ (42,012)						(42,012)
Shares repurchased, shares	(1,223,674)
Balance at Dec. 31, 2019	$ 194,771	$ 52,110	$ 714,051	$ (59,099)	$ 5,154		$ 906,987
Balance, shares at Dec. 31, 2019	109,337,781