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Customer Concentrations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Customer concentrations
Amount	$ 480,883	$ 431,842	$ 337,436	$ 291,573	$ 373,066	$ 375,483	$ 351,956	$ 359,645	$ 1,541,734	$ 1,460,150	$ 941,765
Revenues | Customer concentration
Customer concentrations
Amount									690,670	679,787	389,040
Percentage									44.80%	46.50%	41.20%
Revenues | Customer concentration | Texas DOT
Customer concentrations
Amount									88,783
Percentage									5.80%
Revenues | Customer concentration | Texas DOT | Maximum
Customer concentrations
Percentage										5.00%	5.00%
Revenues | Customer concentration | Public gas and electric utility
Customer concentrations
Amount									224,845	165,373	69,212
Percentage									14.60%	11.30%	7.30%
Revenues | Customer concentration | Gas utility
Customer concentrations
Amount									86,786
Percentage									5.60%
Revenues | Customer concentration | Gas utility | Maximum
Customer concentrations
Percentage										5.00%	5.00%
Revenues | Customer concentration | Private gas and electric utility
Customer concentrations
Amount									106,804
Percentage									6.90%
Revenues | Customer concentration | Private gas and electric utility | Maximum
Customer concentrations
Percentage										5.00%	5.00%
Revenues | Customer concentration | Louisiana DOT
Customer concentrations
Amount									170,899	239,516	193,139
Percentage									11.10%	16.40%	20.50%
Revenues | Customer concentration | Public state agency
Customer concentrations
Amount											47,465
Percentage											5.00%
Revenues | Customer concentration | Public state agency | Maximum
Customer concentrations
Percentage									5.00%	5.00%
Revenues | Customer concentration | Gas utility (Ruby Pipeline Project)
Customer concentrations
Amount									12,553	274,898	79,224
Percentage									0.80%	18.80%	8.40%
Revenues | Customer concentration | Top ten customers
Customer concentrations
Amount									$ 862,300	$ 1,000,000
Percentage									55.90%	68.50%	55.30%
Number of top customers									10
Revenues | Customer concentration | One customer
Customer concentrations
Percentage									14.60%	11.30%
Accounts receivable | Customer concentration | One customer
Customer concentrations
Percentage									10.00%	15.50%
Number of customers									1	1

X

- Definition

Represents the number of customers who typically contribute accounts receivable in excess of a specified percentage.

+ References

No definition available.

+ Details

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X

- Definition

Represents the number of top customers who typically generate revenue in excess of a specified percentage of total revenues for the entity and consist of a different group of customers in each year.

+ References

No definition available.

+ Details

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X

- Definition

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.

+ References

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

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X

- Definition

Aggregate revenue during the period from services rendered in the normal course of business, after deducting 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(d))

-URI http://asc.fasb.org/extlink&oid=6880815&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

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