Marketable Securities - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Marketable Securities [Abstract]
Net unrealized gains (losses)	$ 698,000	$ (647,000)	$ 2,288,000	$ (1,466,000)
Transfers of investments between Level 1 and Level 2	$ 0	$ 0	$ 0	$ 0