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	Sep. 30, 2012	Jun. 30, 2012
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Futures, options and other derivative assets	$ 377	$ 1,626
Derivative liabilities	0	410
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Futures, options and other derivative assets	0	0
Derivative liabilities	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Futures, options and other derivative assets	377	1,626
Derivative liabilities	0	410
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Futures, options and other derivative assets	0	0
Derivative liabilities	0	0
Preferred Stock | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock	20,214	19,395
Preferred Stock | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock	14,856	14,078
Preferred Stock | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock	5,358	5,317
Preferred Stock | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock	$ 0	$ 0