Commitments and Contingencies - Additional Information (Detail)							1 Months Ended	6 Months Ended	9 Months Ended		12 Months Ended
	Dec. 17, 2017 Defendant	Apr. 19, 2017 USD ($) Party	Oct. 05, 2016	Jun. 16, 2016 USD ($)	Mar. 04, 2016 USD ($)	Jul. 07, 2014 Defendant	May 31, 2007 Defendant	Jun. 30, 2018 Defendant	Sep. 30, 2018 USD ($) Defendant	Sep. 30, 2017 USD ($)	Dec. 31, 2015 USD ($)	Jan. 31, 2018 USD ($) Party	Dec. 31, 2017 USD ($)	Mar. 30, 2017 Party	Sep. 30, 2003 Party
Loss Contingencies [Line Items]
Accrued legal matters									$ 12,311,000				$ 12,311,000
Credits for environmental litigation accruals										$ (106,000)
Provisions for environmental litigation accruals									26,000
Legal litigation settlements									$ 147,000
Bankrupty files claim amount		$ 14,000,000
Number of released parties | Party		59
Occidental Chemical Corporation [Member] | EPA [Member]
Loss Contingencies [Line Items]
Number of potentially responsible parties | Party														20
Remedial design performance period under EPA settlement agreement			4 years
Number of potentially responsible parties that the EPA intends to enter into a final settlement agreement with | Party												15
Remediation cost for identified responsible parties												$ 280,600
8 Mile Stretch of Lower Passaic River [Member]
Loss Contingencies [Line Items]
Cost estimate for remediating Lower Passaic River					$ 1,380,000,000
Minimum [Member] | Occidental Chemical Corporation [Member] | CERCLA [Member]
Loss Contingencies [Line Items]
Number of defendants under complaint | Defendant								120
Minimum [Member] | 17 Mile Stretch of Lower Passaic River [Member]
Loss Contingencies [Line Items]
Cost estimate for remediating Lower Passaic River											$ 483,000,000
Maximum [Member] | 17 Mile Stretch of Lower Passaic River [Member]
Loss Contingencies [Line Items]
Cost estimate for remediating Lower Passaic River											$ 725,000,000
Lower Passaic River [Member]
Loss Contingencies [Line Items]
Number of potentially responsible parties | Party															66
Lower Passaic River [Member] | YPF [Member]
Loss Contingencies [Line Items]
Payment of bankruptcy amount				$ 130,000,000
Lower Passaic River [Member] | Minimum [Member] | 17 Mile Stretch of Lower Passaic River [Member]
Loss Contingencies [Line Items]
Parties to perform a remedial investigation and feasibility study | Defendant							70
MTBE [Member] | NJ [Member]
Loss Contingencies [Line Items]
Number of defendants in the MTBE complaint | Defendant									50
MTBE [Member] | Minimum [Member] | PA [Member]
Loss Contingencies [Line Items]
Number of defendants in the MTBE complaint | Defendant						50
MTBE [Member] | Minimum [Member] | MARYLAND [Member]
Loss Contingencies [Line Items]
Number of defendants in the MTBE complaint | Defendant	60