Summary of Significant Accounting Policies - Summary of changes to goodwill by business segment (Details 7) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Goodwill [Line Items]
Gross Balance December 31, 2012	$ 38,971
Accumulated Impairments
Goodwill [Roll Forward]
Balance (net of impairments) December 31, 2012	38,971
Adjustments to Goodwill in 2013
Balance (net of impairments) June 30, 2013	38,971
Manufacturing
Goodwill [Line Items]
Gross Balance December 31, 2012	12,186
Accumulated Impairments
Goodwill [Roll Forward]
Balance (net of impairments) December 31, 2012	12,186
Adjustments to Goodwill in 2013
Balance (net of impairments) June 30, 2013	12,186
Construction
Goodwill [Line Items]
Gross Balance December 31, 2012	7,483
Accumulated Impairments
Goodwill [Roll Forward]
Balance (net of impairments) December 31, 2012	7,483
Adjustments to Goodwill in 2013
Balance (net of impairments) June 30, 2013	7,483
Plastics
Goodwill [Line Items]
Gross Balance December 31, 2012	19,302
Accumulated Impairments
Goodwill [Roll Forward]
Balance (net of impairments) December 31, 2012	19,302
Adjustments to Goodwill in 2013
Balance (net of impairments) June 30, 2013	$ 19,302

Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 68

-Subparagraph l

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 20

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-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph e

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 43

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 72

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph e

-Clause 1

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 34

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

Change in the carrying value of goodwill. The change could be the result of new goodwill acquired, goodwill impairment, if any, goodwill written off related to the sale of a business or other adjustments to goodwill.

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