Investments - Summary of Fair Value of Investments Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017
Assets:
Short-term investments:		$ 30,279
Total assets at fair value	$ 9,377	34,059
Liabilities:
Acquisition-related contingent consideration	2,361	354
Total liabilities at fair value	2,361	354
U.S. Treasury
Assets:
Short-term investments:	3,673	3,894
Corporate debt securities | Financial
Assets:
Short-term investments:	2,843	3,041
Long-term investments:		1,858
Corporate debt securities | Industrial
Assets:
Short-term investments:	2,861	9,503
Long-term investments:		1,922
Commercial paper | Financial
Assets:
Short-term investments:		10,850
Commercial paper | Industrial
Assets:
Short-term investments:		2,991
Quoted Prices in Active Markets (Level 1)
Assets:
Short-term investments:		3,894
Total assets at fair value	3,673	3,894
Liabilities:
Acquisition-related contingent consideration	0	0
Total liabilities at fair value	0	0
Quoted Prices in Active Markets (Level 1) | U.S. Treasury
Assets:
Short-term investments:	3,673	3,894
Quoted Prices in Active Markets (Level 1) | Corporate debt securities | Financial
Assets:
Short-term investments:	0	0
Long-term investments:		0
Quoted Prices in Active Markets (Level 1) | Corporate debt securities | Industrial
Assets:
Short-term investments:	0	0
Long-term investments:		0
Quoted Prices in Active Markets (Level 1) | Commercial paper | Financial
Assets:
Short-term investments:		0
Quoted Prices in Active Markets (Level 1) | Commercial paper | Industrial
Assets:
Short-term investments:		0
Significant Other Observable Inputs (Level 2)
Assets:
Short-term investments:		26,385
Total assets at fair value	5,704	30,165
Liabilities:
Acquisition-related contingent consideration	0	0
Total liabilities at fair value	0	0
Significant Other Observable Inputs (Level 2) | U.S. Treasury
Assets:
Short-term investments:	0	0
Significant Other Observable Inputs (Level 2) | Corporate debt securities | Financial
Assets:
Short-term investments:	2,843	3,041
Long-term investments:		1,858
Significant Other Observable Inputs (Level 2) | Corporate debt securities | Industrial
Assets:
Short-term investments:	2,861	9,503
Long-term investments:		1,922
Significant Other Observable Inputs (Level 2) | Commercial paper | Financial
Assets:
Short-term investments:		10,850
Significant Other Observable Inputs (Level 2) | Commercial paper | Industrial
Assets:
Short-term investments:		2,991
Significant Unobservable Inputs (Level 3)
Assets:
Short-term investments:		0
Total assets at fair value	0	0
Liabilities:
Acquisition-related contingent consideration	2,361	354
Total liabilities at fair value	2,361	354
Significant Unobservable Inputs (Level 3) | U.S. Treasury
Assets:
Short-term investments:	0	0
Significant Unobservable Inputs (Level 3) | Corporate debt securities | Financial
Assets:
Short-term investments:	0	0
Long-term investments:		0
Significant Unobservable Inputs (Level 3) | Corporate debt securities | Industrial
Assets:
Short-term investments:	$ 0	0
Long-term investments:		0
Significant Unobservable Inputs (Level 3) | Commercial paper | Financial
Assets:
Short-term investments:		0
Significant Unobservable Inputs (Level 3) | Commercial paper | Industrial
Assets:
Short-term investments:		$ 0