For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13537-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Commitments and Contingencies (Details 3) (USD $) In Millions, unless otherwise specified						12 Months Ended
	Dec. 31, 2012 Performance bonds	Jul. 09, 2012 Decker Litigation	Dec. 31, 2012 Revenues	Dec. 31, 2011 Revenues	Dec. 31, 2010 Revenues	Dec. 31, 2012 Multi-year contracts Revenues	Dec. 31, 2011 Multi-year contracts Revenues	Dec. 31, 2010 Multi-year contracts Revenues
Concentrations of Risk and Major Customer
Joint venture ownership percentage		50.00%
Percentage required for qualification as major customer			10.00%	10.00%	10.00%
Percentage of revenue						93.00%	81.00%	83.00%
Outstanding amount of surety bonds	$ 610.3