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Amount of increase (decrease) in gross margin due to changes in cost estimates.

No definition available.

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Represent entity's portion of increased project costs.

No definition available.

Name:	chm_IncreasedProjectCosts
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Represents the percentage of completion of the project.

No definition available.

Name:	chm_PercentageOfProjectCompletion
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Represents the profit or loss on the project recorded.

No definition available.

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Cumulative provision for contract losses not offset against related costs accumulated on the balance sheet attributable to the noncontrolling interest.

No definition available.

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Data Type:	xbrli:monetaryItemType
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The total amount of accounts receivable from customers under long-term contracts or programs associated with unapproved change orders or other similar items subject to uncertainty concerning their determination or ultimate realization.

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 210.5-02.3(c)(4))
-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 910
-SubTopic 310
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51673017&loc=d3e49324-109356

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Period Type:	instant

Cumulative provision for contract losses not offset against related costs accumulated on the balance sheet.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 35
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=51671739&loc=d3e57777-111642

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Period Type:	instant

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Namespace Prefix:
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Name:	us-gaap_TypeOfArrangementAxis=chm_FixedPriceContractMember
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Data Type:	na
Balance Type:
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Name:	us-gaap_TypeOfArrangementAxis=chm_ContractWithNoncontrollingJointVenturePartnerMember
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