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Summary of Significant Accounting Policies (Details 3) (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 concentration
Revenues	$ 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 concentration
Revenues									690,670	679,787	389,040
Percentage of concentration risk									44.80%	46.50%	41.20%
Revenues | Customer concentration | Top ten customers
Customer concentration
Number of top customers									10
Number of calendar years in which top customers typically generate minimum specified percentage of revenue									1
Revenues									862,300	1,000,000
Percentage of concentration risk									55.90%	68.50%	55.30%
Revenues | Customer concentration | Top ten customers | Minimum
Customer concentration
Minimum percentage of revenues generated by top ten customers									50.00%
Revenues | Customer concentration | Louisiana DOT
Customer concentration
Revenues									170,899	239,516	193,139
Percentage of concentration risk									11.10%	16.40%	20.50%
Revenues | Customer concentration | Large gas and electric utility
Customer concentration
Percentage of concentration risk									14.60%	11.30%
Revenues | Customer concentration | Ruby contract
Customer concentration
Revenues									$ 12,600	$ 274,900
Percentage of concentration risk									0.80%	18.80%
Revenues | Customer concentration | One customer
Customer concentration
Percentage of concentration risk									14.60%	11.30%
Accounts receivable | Customer concentration | One customer
Customer concentration
Percentage of concentration risk									10.00%	15.50%
Number of customers									1	1

X

- Definition

Represents the minimum percentage of revenue typically generated by specified number of customers in any one calendar year.

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- Definition

Represents the number of calendar years in which top customers typically generate minimum specified percentage of revenue.

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- Definition

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

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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.

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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

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Aggregate revenue during the period from services rendered in the normal course of business, after deducting allowances and discounts.

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