Total Revenues (Revenue from the Rendering of Services) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues	$ 245,346	$ 227,401	$ 814,054	$ 679,441
Service Revenues [Member]
Revenues	161,374	145,938	551,736	442,066
Commission Revenue [Member]
Revenues	87,548	88,696	313,539	280,235
Fees Revenue [Member]
Revenues	73,826	57,242	238,197	161,831
Revenue from Inventory Sales [Member]
Revenues	$ 83,972	$ 81,463	$ 262,318	$ 237,375