Commitments and Contingencies - Additional Information (Detail)					1 Months Ended	6 Months Ended	12 Months Ended
	Dec. 17, 2017 Defendant	Oct. 05, 2016	Mar. 04, 2016 USD ($)	Jul. 07, 2014 Defendant	May 31, 2007 Defendant	Jun. 30, 2018 USD ($) Defendant	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
Litigation losses						(70,000)
Legal litigation settlements						$ 147,000
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] | 17 Mile Stretch of Lower Passaic River [Member]
Loss Contingencies [Line Items]
Cost estimate for remediating Lower Passaic River							$ 483,000,000
Maximum [Member] | Occidental Chemical Corporation [Member] | CERCLA [Member]
Loss Contingencies [Line Items]
Number of defendants under complaint | Defendant						120
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] | Minimum [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