Operating Expenses (Schedule of Acquisition Related Costs) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Continuing employment costs	$ 5,476	$ 6,258
Acquisition-related costs	8,627	1,197
Iron Planet Holdings Inc. [Member]
Acquisition-related costs	7,691
Mascus International Holdings BV [Member]
Continuing employment costs	156	173
Acquisition-related costs		718
Xcira LLC [Member]
Continuing employment costs	381	$ 306
Petrowsky Auctioneers Inc. [Member]
Continuing employment costs	212
Kramer Auctions Ltd. [Member]
Continuing employment costs	115
Acquisition-related costs	$ 72