Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2016		Sep. 30, 2015		Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value Assets, level 1 to level 2 transfers	$ 0				$ 0
Net transfer In (Out) of Level 3 (a)	5,200,000	[1]	$ 19,100,000	[2]	0
Transfers, assets, level 2 to 1			0		0
Transfers, liabilities, level 1 to 2			0		0
Transfers, liabilities, level 2 to 1			0		0
Net transfer level 3			0		30,900,000	[1]
Asset Backed Securities and Corporate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities, Amortized Cost Basis	15,500,000		4,800,000		13,100,000
Available-for-sale Securities	$ 8,100,000		$ 2,500,000		$ 10,100,000
Front Street Future Policyholder Benefits Reserve [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Risk margin for uncertainty			0.50%
Front Street Future Policyholder Benefits Reserve [Member] | Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Risk margin for uncertainty			1.00%

[1] (a) During Fiscal 2016, the net transfer to Level 3 was exclusively from Level 2. The transfers into Level 3 were related to changes in the primary pricing source and changes in the observability of external information used in determining the fair value.

[2] (a) During Fiscal 2015, the net transfer to Level 3 was related to a loan receivable previously classified as a related party loan.