Revenues (Net Profits on Inventory Sales Included in Commissions) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues [Abstract]
Revenue from inventory sales	$ 85,833	$ 111,032	$ 161,881	$ 235,589
Cost of inventory sold	(76,822)	(104,978)	(140,223)	(216,514)
Net profits on inventory	$ 9,011	$ 6,054	$ 21,658	$ 19,075