Quarterly report pursuant to Section 13 or 15(d)

Acquisitions (Details Textual)

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Acquisitions (Details Textual) (USD $)
3 Months Ended 6 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 6 Months Ended 6 Months Ended 6 Months Ended 6 Months Ended
Jun. 30, 2012
Mar. 31, 2012
Entity
Jun. 30, 2012
Dec. 31, 2011
Entity
Jun. 30, 2012
Electric Power Division [Member]
Dec. 31, 2011
Electric Power Division [Member]
Mar. 31, 2012
Electric Power Division [Member]
CANADA
Entity
Dec. 31, 2011
Electric Power Division [Member]
CANADA
Entity
Jun. 30, 2012
Electric Power Division [Member]
UNITED STATES
Entity
Mar. 31, 2012
Electric Power Division [Member]
UNITED STATES
Entity
Dec. 31, 2011
Electric Power Division [Member]
UNITED STATES
Entity
Jun. 30, 2012
Natural Gas and Pipeline Division [Member]
Dec. 31, 2011
Natural Gas and Pipeline Division [Member]
Mar. 31, 2012
Natural Gas and Pipeline Division [Member]
UNITED STATES
Entity
Dec. 31, 2011
Natural Gas and Pipeline Division [Member]
AUSTRALIA
Entity
Dec. 31, 2011
Third and fourth quarters 2011 acquisitions [Member]
Jun. 30, 2012
Phasor [Member]
Mar. 02, 2012
Phasor [Member]
Jun. 30, 2012
Crux [Member]
Jan. 09, 2012
Crux [Member]
Jun. 30, 2012
Microline [Member]
Jan. 04, 2012
Microline [Member]
Jun. 30, 2012
Service Electric [Member]
Apr. 12, 2012
Service Electric [Member]
Acquisitions (Textual) [Abstract]                                                
Cash paid for acquisition                               $ 80,800,000   $ 2,900,000   $ 27,500,000   $ 6,800,000   $ 20,300,000
Number of shares issued for acquisition of company                               1,939,813 87,963   856,105   320,619   662,426  
Common stock value 37,291,000   37,291,000 32,368,000                       32,400,000   1,700,000   16,700,000   6,400,000   12,500,000
Payment of cash to repay acquiree debt                               3,400,000       4,200,000   900,000   5,900,000
Goodwill 64,779,000   64,779,000 43,758,000 57,500,000 34,900,000           7,300,000 8,900,000                      
Number of business acquisitions completed   3   5     1 3 1 1 1     1 1                  
Acquisitions (Additional Textual) [Abstract]                                                
Accounts receivables with fair value 15,300,000   15,300,000 16,100,000                                        
Goodwill expected to be deductible for income tax 52,900,000   52,900,000 13,100,000                                        
Revenues contributed by acquisitions 19,600,000   24,700,000                                          
Income before income taxes contributed by acquisitions $ 700,000   $ 600,000