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
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 14,864	$ 14,517
Fair value adjustments	1,019
Interest accretion	99	437
Foreign currency translation loss (gain)	180	(663)
Ending balance	$ 16,162	$ 14,291