Revolving Credit Facility - Additional Information (Detail) - Revolving Credit Facility [Member]	3 Months Ended
	Dec. 31, 2017 USD ($)
Line Of Credit Facility [Line Items]
Revolving credit facility amount	$ 30,000,000
Credit facility fee percentage	0.15%
Line of credit facility expiration month and year	2019-11
Borrowings outstanding	$ 0
Minimum [Member]
Line Of Credit Facility [Line Items]
Credit facility interest rate	1.00%
Maximum [Member]
Line Of Credit Facility [Line Items]
Credit facility interest rate	1.75%
Multi-currency Overdraft Facility [Member] | Ireland
Line Of Credit Facility [Line Items]
Line of credit facility additional borrowing capacity	$ 5,000,000
Credit facility incremental of additional borrowings	5,000,000
Multi-currency Overdraft Facility [Member] | Maximum [Member] | Ireland
Line Of Credit Facility [Line Items]
Line of credit facility additional borrowing capacity	$ 20,000,000