Fair Value Measurements - Schedule of Contingent Consideration Liabilities Measured at Fair Value (Detail) - Contingent Consideration [Member] - Significant Unobservable Inputs (Level 3) [Member] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 3,326	$ 3,200	$ 14,466
Fair value adjustments	(362)		(511)
Settlements		$ (3,200)	(10,979)
Interest accretion	45		159
Foreign currency translation loss (gain)			(126)
Ending balance	$ 3,009		$ 3,009