INVESTMENTS - SUMMARY OF FAIR VALUE OF INVESTMENTS MEASURED ON A RECURRING BASIS (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	$ 34,059	$ 26,815
Acquisition-related contingent consideration	354	252
Total liabilities at fair value	354	252
Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	30,279	24,863
Short-term investments | US Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	3,894	12,915
Short-term investments | Corporate debt securities | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	3,041	3,963
Short-term investments | Corporate debt securities | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	9,503	4,445
Short-term investments | Commercial paper | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	10,850	2,843
Short-term investments | Commercial paper | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	2,991	697
Long-term investments | US Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0
Long-term investments | Corporate debt securities | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	1,858	502
Long-term investments | Corporate debt securities | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	1,922	1,450
Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	3,894	12,915
Acquisition-related contingent consideration	0	0
Total liabilities at fair value	0	0
Quoted Prices in Active Markets (Level 1) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	3,894	12,915
Quoted Prices in Active Markets (Level 1) | Short-term investments | US Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	3,894	12,915
Quoted Prices in Active Markets (Level 1) | Short-term investments | Corporate debt securities | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Quoted Prices in Active Markets (Level 1) | Short-term investments | Corporate debt securities | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Quoted Prices in Active Markets (Level 1) | Short-term investments | Commercial paper | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Quoted Prices in Active Markets (Level 1) | Short-term investments | Commercial paper | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Quoted Prices in Active Markets (Level 1) | Long-term investments | US Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0
Quoted Prices in Active Markets (Level 1) | Long-term investments | Corporate debt securities | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Quoted Prices in Active Markets (Level 1) | Long-term investments | Corporate debt securities | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	30,165	13,900
Acquisition-related contingent consideration	0	0
Total liabilities at fair value	0	0
Significant Other Observable Inputs (Level 2) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	26,385	11,948
Significant Other Observable Inputs (Level 2) | Short-term investments | US Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Significant Other Observable Inputs (Level 2) | Short-term investments | Corporate debt securities | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	3,041	3,963
Significant Other Observable Inputs (Level 2) | Short-term investments | Corporate debt securities | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	9,503	4,445
Significant Other Observable Inputs (Level 2) | Short-term investments | Commercial paper | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	10,850	2,843
Significant Other Observable Inputs (Level 2) | Short-term investments | Commercial paper | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	2,991	697
Significant Other Observable Inputs (Level 2) | Long-term investments | US Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0
Significant Other Observable Inputs (Level 2) | Long-term investments | Corporate debt securities | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	1,858	502
Significant Other Observable Inputs (Level 2) | Long-term investments | Corporate debt securities | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	1,922	1,450
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Acquisition-related contingent consideration	354	252
Total liabilities at fair value	354	252
Significant Unobservable Inputs (Level 3) | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Short-term investments | US Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Short-term investments | Corporate debt securities | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Short-term investments | Corporate debt securities | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Short-term investments | Commercial paper | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Short-term investments | Commercial paper | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Long-term investments | US Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0
Significant Unobservable Inputs (Level 3) | Long-term investments | Corporate debt securities | Financial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	0	0
Significant Unobservable Inputs (Level 3) | Long-term investments | Corporate debt securities | Industrial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets at fair value	$ 0	$ 0