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.

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

+ Details

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

- 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_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

+ 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

+ Details

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

- Details

Name:	us-gaap_MajorCustomersAxis=cmt_NavistarMember
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_PaccarMember
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:

- Details

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

- Details

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

- Details

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

Major Customers (Details) - USD ($)	3 Months Ended												12 Months Ended
Major Customers (Details) - USD ($)	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Major customers:
Total product sales	$ 43,492,000	$ 44,243,000	$ 53,514,000	$ 47,854,000	$ 42,592,000	$ 43,171,000	$ 43,317,000	$ 40,664,000	$ 36,750,000	$ 32,342,000	$ 32,146,000	$ 32,858,000	$ 189,103,000	$ 169,744,000	$ 134,096,000
Total tooling sales	3,072,000	3,806,000	1,342,000	1,745,000	1,822,000	420,000	2,807,000	411,000	898,000	5,092,000	2,535,000	1,504,000	9,965,000	5,460,000	10,029,000
Total net sales	$ 46,564,000	$ 48,049,000	$ 54,856,000	$ 49,599,000	$ 44,414,000	$ 43,591,000	$ 46,124,000	$ 41,075,000	$ 37,648,000	$ 37,434,000	$ 34,681,000	$ 34,362,000	199,068,000	175,204,000	144,125,000
Navistar
Major customers:
Total net sales													56,415,000	51,330,000	47,356,000
Volvo [Member]
Major customers:
Total net sales													55,125,000	48,859,000	12,444,000
Paccar
Major customers:
Total net sales													34,430,000	36,128,000	50,154,000
Yamaha [Member]
Major customers:
Total net sales													16,766,000	16,911,000	13,648,000
Other customers
Major customers:
Total net sales													36,332,000	21,976,000	20,523,000
Product sales
Major customers:
Total net sales													189,103,000	169,744,000	134,096,000
Product sales \| Navistar
Major customers:
Total net sales													50,169,000	51,254,000	46,384,000
Product sales \| Volvo [Member]
Major customers:
Total net sales													53,525,000	46,340,000	11,508,000
Product sales \| Paccar
Major customers:
Total net sales													33,452,000	35,602,000	42,784,000
Product sales \| Yamaha [Member]
Major customers:
Total net sales													16,766,000	16,911,000	13,648,000
Product sales \| Other customers
Major customers:
Total net sales													35,191,000	19,637,000	19,772,000
Tooling sales
Major customers:
Total net sales													9,965,000	5,460,000	10,029,000
Tooling sales \| Navistar
Major customers:
Total net sales													6,246,000	76,000	972,000
Tooling sales \| Volvo [Member]
Major customers:
Total net sales													1,600,000	2,519,000	936,000
Tooling sales \| Paccar
Major customers:
Total net sales													978,000	526,000	7,370,000
Tooling sales \| Yamaha [Member]
Major customers:
Total net sales													0	0	0
Tooling sales \| Other customers
Major customers:
Total net sales													$ 1,141,000	$ 2,339,000	$ 751,000