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, 2018	Mar. 31, 2019	Mar. 31, 2018
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 3,326	$ 16,162	$ 14,466	$ 14,864
Fair value adjustments	(362)	(2,317)	(511)	(1,298)
Settlements		(925)	(10,979)	(925)
Interest accretion	45	87	159	186
Foreign currency translation loss (gain)		338	(126)	518
Ending balance	$ 3,009	$ 13,345	$ 3,009	$ 13,345