Reportable Segment Information - Geographic Revenue and Long-lived Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
U.S. [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets, including property and equipment and intangible assets net of accumulated depreciation and amortization	$ 24,450	$ 26,652
Ireland [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets, including property and equipment and intangible assets net of accumulated depreciation and amortization	$ 19,524	$ 21,174
Revenue [Member] | Geographic Concentration Risk [Member] | Domestic [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of revenue	81.00%	79.00%	77.00%
Revenue [Member] | Geographic Concentration Risk [Member] | Foreign [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage of revenue	19.00%	21.00%	23.00%