Operating Expenses (Schedule of Acquisition Related Costs) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Continuing employment costs	$ 9,019	$ 5,476
Other acquisition-related costs	1,633	8,627
Iron Planet Holdings Inc. [Member]
Other acquisition-related costs	639	7,691
Other Acquisitions [Member]
Continuing employment costs	968	864
Other acquisition-related costs	$ 26	$ 72

Payroll costs incurred (including equity-based compensation) that are directly related to services rendered by an entity during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(d))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_CostOfServicesDirectLabor
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration