Investments, deposits and other assets (Schedule of Realized Gains and Losses) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2011	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2010
Investments, deposits and other assets [Abstract]
Realized gains		$ 8		$ 139		$ 281
Realized losses			[1]	(1,685)	[1]	(40)	[1]
Net gain (loss)		8		(1,546)		241
Recorded cooperative allocated surplus	$ 1,685

[1] During the second quarter of 2011, the Company fully reserved $1,685,000 in cooperative allocated surplus it had recorded based on its patronage allocation with Farm Credit.