Inventories, Net - Supplemental Inventory Information (Details) $ in Thousands	Jun. 30, 2020 USD ($) $ / oz	Dec. 31, 2019 USD ($) $ / oz
Inventory Disclosure [Abstract]
Precious metals stated at LIFO cost | $	$ 2,849	$ 15,660
Precious metals stated under non-LIFO cost methods, primarily at fair value | $	$ 20,966	$ 10,144
Market value per ounce, Silver (in dollars per ounce)	17.88	17.86
Market value per ounce, Gold (in dollars per ounce)	1,767.93	1,522.14
Market value per ounce, Palladium (in dollars per ounce)	1,894.23	1,935.19