A-Mark Precious Metals, Inc. Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies (Derivative Instruments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Realized loss on future commodity contracts, net	$ (28,166)	$ 7,567	$ (34,522)	$ (10,022)
Futures Commodity And Forwards Contracts And Open Purchase And Sale Commitments [Member]
Derivative [Line Items]
Unrealized gain (loss) on open future commodity and forward contracts and open sale and purchase commitments, net	9,006	14,047	10,284	(1,839)
Commodity Contract
Derivative [Line Items]
Realized loss on future commodity contracts, net	$ (37,172)	$ (6,480)	$ (44,806)	$ (8,183)