Summary of Significant Accounting Policies and Select Balance Sheet Information - Sales of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Investments Debt And Equity Securities [Abstract]
Proceeds from sales	$ 44,853	$ 43,556	$ 50,364
Gross realized gains	179	229	384
Gross realized losses	$ (43)	$ (1)	$ (4)