Intangible Assets Subject to Amortization (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 379,042	$ 378,831
Accum. Amortization	283,168	273,613
Net	95,874	105,218
Customer Lists
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	346,995	346,784
Accum. Amortization	272,118	264,632
Net	74,877	82,152
Trade Names And Other Intangibles
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	32,047	32,047
Accum. Amortization	11,050	8,981
Net	$ 20,997	$ 23,066