Inventories (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Inventories [Abstract]
Terms of precious metals consignment agreements, maximum			1 year
Fees under precious metals consignment agreements	$ 0.4	$ 0.3	$ 0.8	$ 0.5
Fair value of precious metals on hand under consignment agreements	$ 44.1		$ 44.1		$ 37.7