Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Schedule of Available-for-sale Securities [Line Items]
Long-term marketable securities	$ 65,013	$ 16,389
Short Term Marketable Securities [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	1 year
Corporate Bonds and U.S. Treasury Notes [Member] | Long Term Marketable Securities [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	3 years
Corporate Bonds and U.S. Treasury Notes [Member] | Long Term Marketable Securities [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	1 year