Inventories (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Inventories [Abstract]
Terms of precious metals consignment agreements, maximum	1 year
Fees under precious metals consignment agreements	$ 0.4	$ 0.2
Fair value of precious metals on hand under consignment agreements	$ 39.6		$ 37.7