Schedule of Financial Instruments Where Carrying Value and Fair Value Differ (Detail) $ in Millions	Sep. 30, 2017 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Long-term obligations, excluding capital leases	$ 92.0
Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Long-term obligations, excluding capital leases	0.0
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Long-term obligations, excluding capital leases	92.8
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Long-term obligations, excluding capital leases	$ 0.0