Investments and Derivative Instruments - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Jun. 30, 2011
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Futures, options and other derivative assets	$ 1,626	[1]	$ 467	[1]
Derivative liabilities	410	[2]	1,647	[2]
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Futures, options and other derivative assets	0	[1]	0	[1]
Derivative liabilities	0	[2]	0	[2]
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Futures, options and other derivative assets	1,626	[1]	467	[1]
Derivative liabilities	410	[2]	1,647	[2]
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Futures, options and other derivative assets	0	[1]	0	[1]
Derivative liabilities	0	[2]	0	[2]
Preferred Stock | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	19,395	[1]	24,407	[1]
Preferred Stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	14,078	[1]	7,181	[1]
Preferred Stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	5,317	[1]	17,226	[1]
Preferred Stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	$ 0	[1]	$ 0	[1]

[1] Included in "Short-term investments" on the consolidated balance sheet.

[2] Included in "Accounts Payable" on the consolidated balance sheet.