Major Customers (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Revenue, Major Customer [Line Items]
Total sales	$ 49,599,000us-gaap_SalesRevenueNet	$ 41,075,000us-gaap_SalesRevenueNet
Total product sales	47,854,000us-gaap_SalesRevenueGoodsNet	40,664,000us-gaap_SalesRevenueGoodsNet
Total tooling sales	1,745,000us-gaap_ContractsRevenue	411,000us-gaap_ContractsRevenue
Navistar [Member]
Revenue, Major Customer [Line Items]
Total sales	12,823,000	12,713,000
Volvo [Member]
Revenue, Major Customer [Line Items]
Total sales	14,648,000	10,246,000
Paccar [Member]
Revenue, Major Customer [Line Items]
Total sales	10,349,000	8,392,000
Yamaha [Member]
Revenue, Major Customer [Line Items]
Total sales	5,233,000	5,000,000
Other Customers [Member]
Revenue, Major Customer [Line Items]
Total sales	6,546,000	4,724,000
Product Sales [Member] \| Navistar [Member]
Revenue, Major Customer [Line Items]
Total sales	12,808,000	12,702,000
Product Sales [Member] \| Volvo [Member]
Revenue, Major Customer [Line Items]
Total sales	13,629,000	10,075,000
Product Sales [Member] \| Paccar [Member]
Revenue, Major Customer [Line Items]
Total sales	9,714,000	8,187,000
Product Sales [Member] \| Yamaha [Member]
Revenue, Major Customer [Line Items]
Total sales	5,233,000	5,000,000
Product Sales [Member] \| Other Customers [Member]
Revenue, Major Customer [Line Items]
Total sales	6,470,000	4,700,000
Tooling Sales [Member] \| Navistar [Member]
Revenue, Major Customer [Line Items]
Total sales	15,000	11,000
Tooling Sales [Member] \| Volvo [Member]
Revenue, Major Customer [Line Items]
Total sales	1,019,000	171,000
Tooling Sales [Member] \| Paccar [Member]
Revenue, Major Customer [Line Items]
Total sales	635,000	205,000
Tooling Sales [Member] \| Yamaha [Member]
Revenue, Major Customer [Line Items]
Total sales	0	0
Tooling Sales [Member] \| Other Customers [Member]
Revenue, Major Customer [Line Items]
Total sales	$ 76,000	$ 24,000

Revenue earned during the period arising from products sold or services provided under the terms of a contract, not elsewhere specified in the taxonomy. May include government contracts, construction contracts, and any other contract related to a particular project or product.

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

- Details

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

- Definition

Aggregate revenue during the period from the sale of goods in the normal course of business, after deducting returns, allowances and discounts.

+ 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(a))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

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

- Definition

Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ 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=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

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

- Details

Name:	cmt_SalesByProductTypeAxis=cmt_ProductSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	cmt_SalesByProductTypeAxis=cmt_ToolingSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorCustomersAxis=cmt_NavistarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorCustomersAxis=cmt_OtherCustomersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorCustomersAxis=cmt_PaccarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorCustomersAxis=cmt_VolvoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorCustomersAxis=cmt_YamahaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: