Operating Expenses (Schedule of Acquisition Related Costs) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Costs of services	$ 10,170	$ 10,032	$ 30,120	$ 24,321
Other acquisition-related costs	2,007	3,587	5,039	35,162
Iron Planet Holdings Inc. [Member]
Other acquisition-related costs	1,756	2,712	2,876	32,591
Other Acquisitions [Member]
Costs of services	$ 251	829	2,104	2,421
Other acquisition-related costs		$ 46	$ 59	$ 150