Intangible Assets Subject to Amortization (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 420,324	$ 420,112
Accum. Amortization	330,031	312,424
Net	90,293	107,688
Customer Lists
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	382,942	382,373
Accum. Amortization	312,928	297,221
Net	70,014	85,152
Trade Names And Other Intangibles
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	37,382	37,739
Accum. Amortization	17,103	15,203
Net	$ 20,279	$ 22,536