Represents the period of time for the reporting lag relating to joint venture to achieve a timely consolidation, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

+ Details

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Namespace Prefix:	chm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(a),(d))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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

- Details

Name:	us-gaap_ErrorCorrectionsAndPriorPeriodAdjustmentsRestatementByRestatementPeriodAndAmountAxis=chm_PreviouslyExistingOneMonthReportingLagMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_RestatementAdjustmentMember
Namespace Prefix:
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Segment Information - Adjustment to Revenue and Direct Cost of Services (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2016	Sep. 30, 2016	Jun. 24, 2016	Mar. 25, 2016	Dec. 25, 2015	Sep. 25, 2015	Jun. 26, 2015	Mar. 27, 2015	Dec. 30, 2016	Dec. 25, 2015	Dec. 31, 2014
Segment Information
Period of reporting lag to achieve timely consolidation									1 month
Revenues	$ 1,315,083	$ 1,302,609	$ 1,290,965	$ 1,287,010	$ 1,332,796	$ 1,303,978	$ 1,284,652	$ 1,228,355	$ 5,195,667	$ 5,149,781	$ 5,216,524
Direct cost of services									4,288,408	$ 4,144,293	$ 4,112,330
Previously existing one-month reporting lag \| Adjustment
Segment Information
Revenues									51,700
Direct cost of services									$ 51,700