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, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 16,162	$ 14,291	$ 14,864	$ 14,517
Fair value adjustments	(2,317)	(1,159)	(1,298)	(1,159)
Settlements	(925)		(925)
Interest accretion	87	548	186	985
Foreign currency translation loss (gain)	338	190	518	(473)
Ending balance	$ 13,345	$ 13,870	$ 13,345	$ 13,870