Commitments, Contingencies and Other Matters (Narrative) (Detail) $ in Thousands	6 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($) Entity	Dec. 31, 2016 USD ($)	Jun. 30, 2009 USD ($)	Jun. 30, 2017 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Environmental charge	$ 902	$ 170
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	5,749			$ 8,451
Arsynco | Minimum
Commitments and Contingencies Disclosure [Line Items]
Estimated cost of environmental remediation obligations	21,500
Arsynco | Maximum
Commitments and Contingencies Disclosure [Line Items]
Estimated cost of environmental remediation obligations	23,300
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	2,587			$ 3,803
Subsidiary
Commitments and Contingencies Disclosure [Line Items]
Amount expected to be paid for product registrations and various task force groups	$ 2,324
Berry's Creek Study Area | Arsynco
Commitments and Contingencies Disclosure [Line Items]
Number of potentially responsible parties | Entity	150