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		9 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Derivative [Line Items]
Realized gain (loss) on future commodity contracts, net	$ (10,309)	$ (21,122)	$ (44,831)	$ (31,144)
Futures Commodity And Forwards Contracts And Open Purchase And Sale Commitments [Member]
Derivative [Line Items]
Unrealized loss on open future commodity and forward contracts and open sale and purchase commitments, net	(12,866)	(19,373)	(2,582)	(21,212)
Commodity Contract
Derivative [Line Items]
Realized gain (loss) on future commodity contracts, net	$ 2,557	$ (1,749)	$ (42,249)	$ (9,932)