Fair Value Measurements - Reconciliation of Financial Assets Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Jun. 30, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 24
Transfers into Level 3
Transfers out of Level 3	(24)
Total realized and unrealized gains (losses):
Included in other comprehensive (loss) income
Purchases, issuances, sales and settlements, net
Mortgage-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	15
Transfers into Level 3
Transfers out of Level 3	(15)
Total realized and unrealized gains (losses):
Included in other comprehensive (loss) income
Purchases, issuances, sales and settlements, net
Asset-backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	9
Transfers into Level 3
Transfers out of Level 3	(9)
Total realized and unrealized gains (losses):
Included in other comprehensive (loss) income
Purchases, issuances, sales and settlements, net