INVESTMENTS - SUMMARY OF INVESTMENTS BY TYPE OF SECURITY (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost	$ 34,075	$ 26,810
Gross Unrealized Gains	0	11
Gross Unrealized Losses	(16)	(6)
Fair Market Value	34,059	26,815
US Treasury | Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Cost	3,897	12,907
Gross Unrealized Gains	0	8
Gross Unrealized Losses	(3)	0
Fair Market Value	3,894	12,915
Corporate debt securities | Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Cost	26,393	11,949
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(8)	(3)
Fair Market Value	26,385	11,948
Corporate debt securities | Long-term investments
Schedule of Available-for-sale Securities [Line Items]
Cost	3,785	1,954
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(5)	(3)
Fair Market Value	$ 3,780	$ 1,952