Defined Contribution Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Contribution Plan Disclosure [Line Items]
Contributions to defined contribution plans	$ 1.0	$ 0.9	$ 0.7
U.S. [Member] | 401 (K) Retirement and Savings Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of employee contributions, eligible for employer match	50.00%
Percentage of employee contributions	6.00%
Ireland [Member] | Defined Contribution PRSA Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of employee contributions, eligible for employer match	6.00%
Percentage of employee contributions	8.00%