Business Combinations (Schedule of Net Cash Flows and Purchase Price) (Details) - Iron Planet Holdings Inc. [Member] - USD ($) $ in Thousands		12 Months Ended
	May 31, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Cash consideration paid to former equity holders	$ 723,810
Settlement of IronPlanet's debt	36,313
Settlement of IronPlanet's transaction costs	12,583
Cash consideration paid on closing	772,706
Less: cash and cash equivalents acquired	(95,626)
Less: restricted cash acquired	(3,000)
Acquisition of IronPlanet, net of cash acquired	675,851	$ 675,851
Replacement stock option awards attributable to pre-combination services	4,926
Stock option compensation expense from accelerated vesting of awards attributable to post-combination services	(2,596)
Cash consideration paid relating to closing adjustments	1,771
Settlement of pre-existing intercompany balances	(333)
Total fair value at acquisition date	$ 776,474