Long-Term Debt and Bank Facility Borrowings - Company's Debt (Detail) - USD ($) $ in Thousands		Mar. 31, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Long-term debt, carrying Amount		$ 211,857	$ 100,780
Current maturities of long-term debt, carrying Amount		125,000	9,000
Long-term debt		86,857	91,780
Long-term debt, fair value	[1]	212,500	101,500
Current maturities of long-term debt, fair value	[1]	125,000	9,000
Long-term portion of debt, fair value	[1]	87,500	92,500
Revolving Credit Facility
Debt Instrument [Line Items]
Credit facility borrowings, carrying Amount		115,000	1,500
Credit facility borrowings, fair value	[1]	115,000	1,500
Term Loan
Debt Instrument [Line Items]
Long-term debt, carrying Amount	[2]	96,857	99,280
Long-term debt, fair value	[1],[2]	$ 97,500	$ 100,000

[1] The face amount of the Company’s variable rate long-term debt approximates fair value.

[2] Carrying amounts are net of unamortized debt issuance costs of $0.6 million as of March 31, 2019 and $0.7 million as of September 30, 2018.