Acquisitions (Narrative) (Details) (USD $)	12 Months Ended			0 Months Ended			3 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 14, 2014	Sep. 02, 2014	Oct. 08, 2013	Dec. 31, 2013	Apr. 12, 2013	Feb. 28, 2013	May 20, 2013	Jun. 05, 2012	Jun. 02, 2012	Mar. 04, 2015
Business Acquisition [Line Items]
General and administrative expense	$ 56,419,000	$ 47,071,000	$ 36,201,000
Goodwill	40,210,000	30,226,000	12,884,000				30,226,000
Additional contingent consideration expense	100,000
Acquisition related costs		100,000
Value of common stock share on day of acquisition								$ 12.52
Mission Critical Energy Services [Member]
Business Acquisition [Line Items]
Date of acquisition	Oct. 14, 2014
Cash paid				13,000,000
Working capital adjustment				70,000
Contingent consideration				1,872,000
Indemnification cap				3,000,000
Goodwill				9,379,000
Revenue of the acquiree since date of acquisition	2,700,000
Income (loss) of the acquiree since date of acquisition	(400,000)
Acquisition related costs	100,000
Aggregate acquisition-related costs excluded from Proforma	100,000
Mission Critical Energy Services [Member] | Backlog In The Amount Of At Least $5 Million [Member]
Business Acquisition [Line Items]
Contingent consideration				1,000,000
Mission Critical Energy Services [Member] | Backlog In The Amount Of At Least $15 Million [Member]
Business Acquisition [Line Items]
Contingent consideration				2,000,000
Mission Critical Energy Services [Member] | Noncompete Agreement [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets, useful life	5 years
Apex [Member]
Business Acquisition [Line Items]
Date of acquisition	Sep. 02, 2014
Cash paid					750,000
Contingent consideration					340,000
Goodwill					605,000
Additional contingent consideration expense					500,000
Revenue of the acquiree since date of acquisition					400,000
Income (loss) of the acquiree since date of acquisition					(33,000)
Encari [Member]
Business Acquisition [Line Items]
Date of acquisition	Oct. 08, 2013
Cash paid						4,764,000
Goodwill						1,988,000
Revenue of the acquiree since date of acquisition							700,000
Income (loss) of the acquiree since date of acquisition							200,000
Acquisition related costs	100,000	100,000
Solais Lighting [Member]
Business Acquisition [Line Items]
Date of acquisition	Apr. 12, 2013
Cash paid								6,535,000
Goodwill								11,323,000
Revenue of the acquiree since date of acquisition	5,900,000
Income (loss) of the acquiree since date of acquisition	(1,600,000)
Acquisition related costs	400,000
Working capital deficit								200,000
Common stock issued								675,160
Value per share								$ 12.22
Number of days immediately preceding date of merger								5 days
Cash held in escrow	1,500,000
Escrow holding period	2 years
Increase (decrease) in goodwill	100,000
(Decrease) in purchase price allocated to inventory	(100,000)
Energy Efficiency Services [Member]
Business Acquisition [Line Items]
Date of acquisition	Feb. 28, 2013
Cash paid									1,971,000
Goodwill									3,694,000
Revenue of the acquiree since date of acquisition	28,300,000
Income (loss) of the acquiree since date of acquisition	2,300,000
Acquisition related costs	100,000
Length of non-competition covenants	5 years
Aggregate acquisition-related costs excluded from Proforma	100,000
PowerLine [Member]
Business Acquisition [Line Items]
Date of acquisition	May 20, 2013
Cash paid										550,000
Goodwill										337,000
Revenue of the acquiree since date of acquisition	0
Acquisition related costs	600,000
Annual cash installment payments	100,000
Payment period	5 years
PowerSecure Solar [Member]
Business Acquisition [Line Items]
Date of acquisition	Jun. 02, 2012
Cash paid										200,000	3,523,000
Goodwill											4,914,000
Revenue of the acquiree since date of acquisition			8,200,000
Income (loss) of the acquiree since date of acquisition			100,000
Acquisition related costs			100,000
Non-controlling interest in PowerSecure Solar											433,000
Length of non-competition covenants	5 years
Percentage of majority ownership												90.00%
Percentage of controlling ownership										10.00%
Noncontrolling ownership percentage												10.00%
PowerSecure And Solais [Member]
Business Acquisition [Line Items]
Aggregate acquisition-related costs excluded from Proforma		1,200,000
Lesco And Lime [Member]
Business Acquisition [Line Items]
Length of non-competition covenants	5 years
Minimum [Member] | Mission Critical Energy Services [Member] | Backlog In The Amount Of At Least $5 Million [Member]
Business Acquisition [Line Items]
Intangible asset amount				5,000,000
Minimum [Member] | Mission Critical Energy Services [Member] | Backlog In The Amount Of At Least $15 Million [Member]
Business Acquisition [Line Items]
Intangible asset amount				15,000,000
Subsequent Event [Member] | Mission Critical Energy Services [Member]
Business Acquisition [Line Items]
Consideration owed													$ 1,000,000