Intangible Assets (Parenthetical) (Detail)	6 Months Ended	12 Months Ended
	Jan. 31, 2018	Jul. 31, 2017
Minimum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets		15 years
Maximum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets		20 years
Electronic chemicals-value of product qualifications | Minimum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets	5 years	5 years
Electronic chemicals-value of product qualifications | Maximum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets	15 years	15 years
Performance materials-customer relationships | Minimum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets	15 years
Performance materials-customer relationships | Maximum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets	20 years
Performance materials-proprietary manufacturing process
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets	15 years	15 years
Electronic chemicals-other | Minimum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets	1 year	1 year
Electronic chemicals-other | Maximum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets	15 years	15 years
Performance materials-other | Minimum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets	5 years	5 years
Performance materials-other | Maximum
Finite Lived Intangible Assets [Line Items]
Estimated useful lives of intangible assets	15 years	15 years