Derivative Instruments and Hedging Activities - Balance Sheet Location and Fair Value of Derivative Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Jun. 30, 2014	[1]
Derivative assets:
Derivative assets	$ 1,979	$ 2,516
Derivative liabilities:
Derivative liabilities	(4,995)	(844)
Commodity Contracts | Derivatives Subject to PGC and DS Mechanisms
Derivative assets:
Derivative assets	1,943	2,450
Derivative liabilities:
Derivative liabilities	(4,807)	(844)
Commodity Contracts | Derivatives Not Subject To PGC And DS Mechanisms
Derivative assets:
Derivative assets	36	66
Derivative liabilities:
Derivative liabilities	$ (188)	$ 0

[1] Certain immaterial amounts have been revised to correct the classification of derivatives.