Intangible Assets Subject to Amortization (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 379,042	$ 378,831
Accum. Amortization	278,399	273,613
Net	100,643	105,218
Customer Lists
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	346,995	346,784
Accum. Amortization	268,362	264,632
Net	78,633	82,152
Trade Names And Other Intangibles
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	32,047	32,047
Accum. Amortization	10,037	8,981
Net	$ 22,010	$ 23,066