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Acquisitions - Additional Information (Detail) (USD $)
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12 Months Ended | 12 Months Ended | 12 Months Ended | 1 Months Ended | 1 Months Ended | 12 Months Ended | |||||||||||||
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Dec. 31, 2012
Entity
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Dec. 31, 2011
Entity
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Dec. 31, 2010
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Dec. 31, 2012
Electric Power Division [Member]
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Dec. 31, 2011
Electric Power Division [Member]
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Dec. 31, 2012
Electric Power Division [Member]
Canada [Member]
Entity
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Dec. 31, 2011
Electric Power Division [Member]
Canada [Member]
Entity
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Dec. 31, 2012
Electric Power Division [Member]
United States [Member]
Entity
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Dec. 31, 2011
Electric Power Division [Member]
United States [Member]
Entity
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Dec. 31, 2012
Natural Gas and Pipeline Division [Member]
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Dec. 31, 2011
Natural Gas and Pipeline Division [Member]
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Dec. 31, 2012
Natural Gas and Pipeline Division [Member]
United States [Member]
Entity
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Dec. 31, 2011
Natural Gas and Pipeline Division [Member]
Australia [Member]
Entity
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Oct. 25, 2010
Common Stock and Exchangeable Shares [Member]
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Oct. 31, 2010
Valard Construction LP [Member]
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Oct. 25, 2010
Valard Construction LP [Member]
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Oct. 31, 2010
Valard Construction LP [Member]
Exchangeable Shares [Member]
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Dec. 31, 2012
First and Second Quarters of 2012 acquisitions [Member]
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Dec. 31, 2011
Third and Fourth Quarters of 2011 acquisitions [Member]
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| Business Acquisition [Line Items] | |||||||||||||||||||
| Number of business acquisitions completed | 4 | 5 | 1 | 3 | 2 | 1 | 1 | 1 | |||||||||||
| Cash paid for acquisition | $ 118,900,000 | $ 57,500,000 | $ 80,800,000 | ||||||||||||||||
| Number of shares issued for acquisition of company | 623,720 | 3,909,110 | 1,927,113 | 1,939,813 | |||||||||||||||
| Common stock value | 83,400,000 | 37,291,000 | 32,368,000 | ||||||||||||||||
| Payment of cash to repay acquire debt | 12,800,000 | 11,000,000 | 3,400,000 | ||||||||||||||||
| Accounts receivables with fair value | 15,300,000 | 16,100,000 | |||||||||||||||||
| Goodwill | 57,500,000 | 34,900,000 | 7,300,000 | 8,900,000 | |||||||||||||||
| Goodwill expected to be deductible for income tax | 52,900,000 | 13,100,000 | |||||||||||||||||
| Revenues contributed by acquisitions | 125,700,000 | 43,800,000 | 25,700,000 | ||||||||||||||||
| Income before income taxes contributed by acquisitions | $ 6,200,000 | $ 4,400,000 | $ 3,400,000 | ||||||||||||||||