Commitments, Contingencies and Other Matters (Narrative) (Detail) shares in Thousands, $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 21, 2016 USD ($) shares	Sep. 30, 2018 USD ($) Entity shares	Sep. 30, 2017 USD ($) shares	Jun. 30, 2009 USD ($)	Jun. 30, 2018 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Environmental charge			$ 902
Number of shares to be issued | shares		5,122	5,122
Contingent consideration		$ 703			$ 683
Citron and Lucid
Commitments and Contingencies Disclosure [Line Items]
Deferred payment	$ 50,000
Interest rate	5.00%
Number of shares to be issued | shares	5,122		5,122
Purchase price, earn-out period	5 years
Purchase price, earn-out amount	$ 50,000
Contingent consideration		703			683
PRP Group
Commitments and Contingencies Disclosure [Line Items]
Loss contingency, damages sought		1,700
Arsynco
Commitments and Contingencies Disclosure [Line Items]
Accrual for environmental loss contingencies		$ 4,943			5,746
Arsynco | Berry's Creek Study Area
Commitments and Contingencies Disclosure [Line Items]
Number of potentially responsible parties | Entity		150
Arsynco | Agreement to sell the Arsynco property | Environmental Remediation property for sale
Commitments and Contingencies Disclosure [Line Items]
Expected sale of property value					6,340
Arsynco | Minimum
Commitments and Contingencies Disclosure [Line Items]
Estimated cost of environmental remediation obligations		$ 22,900
Arsynco | Maximum
Commitments and Contingencies Disclosure [Line Items]
Estimated cost of environmental remediation obligations		24,700
BASF
Commitments and Contingencies Disclosure [Line Items]
Partial reimbursement of environmental remediation costs previously expensed				$ 550
Gain related to partial reimbursement				550
Environmental remediation costs expensed in prior years				$ 1,200
Future remediation costs receivable		2,224			$ 2,586
Subsidiary
Commitments and Contingencies Disclosure [Line Items]
Amount expected to be paid for product registrations and various task force groups		$ 5,616