Investments - Sales of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Investments Debt And Equity Securities [Abstract]
Proceeds from sales	$ 65,455	$ 8,507	$ 157,970	$ 34,487
Gross realized gains		6	126	171
Gross realized losses		$ (4)	$ (1)	$ (4)