Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Schedule Of Significant Accounting Policies [Line Items]
Advertising and direct mail expenses	$ 14,500,000	$ 12,500,000	$ 10,500,000
Subsidiaries of Swiss Re
Schedule Of Significant Accounting Policies [Line Items]
Weather hedge contract, payment entitled to be received per heating degree-day shortfall	$ 35,000
Percentage in heating degree days less than ten year average that is covered	92.50%
Derivative maximum payout	$ 12,500,000
Maximum
Schedule Of Significant Accounting Policies [Line Items]
Cash equivalents, highly liquid investments maturity	3 months
Customer Lists
Schedule Of Significant Accounting Policies [Line Items]
Intangible assets, amortization period	7 years
Customer Lists | Maximum
Schedule Of Significant Accounting Policies [Line Items]
Intangible assets, amortization period	10 years
Customer Lists | Minimum
Schedule Of Significant Accounting Policies [Line Items]
Intangible assets, amortization period	7 years
Trade Names | Maximum
Schedule Of Significant Accounting Policies [Line Items]
Intangible assets, amortization period	20 years
Trade Names | Minimum
Schedule Of Significant Accounting Policies [Line Items]
Intangible assets, amortization period	7 years