Current ratio.

No definition available.

Name:	kmg_CurrentRatio
Namespace Prefix:	kmg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fixed charge coverage ratio.

+ References

No definition available.

+ Details

Name:	kmg_FixedChargeCoverageRatio
Namespace Prefix:	kmg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility additional borrowing capacity.

+ References

No definition available.

+ Details

Name:	kmg_LineOfCreditFacilityAdditionalBorrowingCapacity
Namespace Prefix:	kmg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Ratio of indebtedness to earnings before interest taxes depreciation and amortization margin maximum.

+ References

No definition available.

+ Details

Name:	kmg_RatioOfIndebtednessToEarningsBeforeInterestTaxesDepreciationAndAmortizationMarginMaximum
Namespace Prefix:	kmg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Ratio of indebtedness to earnings before interest taxes depreciation and amortization margin maximum extraordinary items adjustment step up during acquisition period.

+ References

No definition available.

+ Details

Name:	kmg_RatioOfIndebtednessToEarningsBeforeInterestTaxesDepreciationAndAmortizationMarginMaximumExtraordinaryItemsAdjustmentStepUpDuringAcquisitionPeriod
Namespace Prefix:	kmg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=kmg_SealweldCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kmg_SecondRestatedCreditFacilityMember
Namespace Prefix:
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Period Type:

Long-Term Debt - Additional Information (Detail) - USD ($)		6 Months Ended
	Feb. 02, 2017	Jan. 31, 2017	Jan. 31, 2016	Oct. 09, 2014
Debt Instrument [Line Items]
Fixed charge coverage ratio		150.00%
Ratio of funded debt to EBITDA maximum		325.00%
Current ratio		150.00%
Ratio of funded debt to EBITDA maximum, step-up during an acquisition period with lender's consent		350.00%
Revolving Loan Facility
Debt Instrument [Line Items]
Line of credit facility, outstanding		$ 41,000,000
Maximum available amount of remaining revolving facility net of unused letter of credit			$ 106,300,000
Reduction credit capacity due to unused letters of credit			$ 2,700,000
Revolving Loan Facility \| Maximum
Debt Instrument [Line Items]
Percentage of unused commitment fee on unused amount of commitments under revolving loan facility		0.30%
Revolving Loan Facility \| Minimum
Debt Instrument [Line Items]
Percentage of unused commitment fee on unused amount of commitments under revolving loan facility		0.15%
Revolving Loan Facility \| Senior Secured Debt
Debt Instrument [Line Items]
Line of credit facility, outstanding		$ 24,000
Line of credit facility, outstanding interest rate		1.776%
Revolving Loan Facility \| Senior Secured Debt \| Sealweld Corporation
Debt Instrument [Line Items]
Line of credit facility, outstanding		$ 17,000,000
Debt instrument, interest at base rate		3.75%
Debt instrument interest rate, description		Three days later on February 2, 2017, the base rate loan was converted to a LIBOR rate loan at an interest rate of 1.776%.
Revolving Loan Facility \| Senior Secured Debt \| Sealweld Corporation \| London Interbank Offered Rate (LIBOR) \| Subsequent Event
Debt Instrument [Line Items]
Variable interest rate	1.779%
Revolving Loan Facility \| Second Restated Credit Facility \| Senior Secured Debt
Debt Instrument [Line Items]
Maximum amount of revolving facility				$ 150,000,000
Amount of cash available under contractual agreement with lender's approval				$ 100,000,000
Loan facility maturity date		Oct. 09, 2019