Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash paid for:
Interest	$ 1,326,000	$ 1,720,000	$ 1,215,000
Income taxes for continuing operations	13,948,000	1,613,000	9,034,000
Income taxes for discontinued operations	5,000	8,000	2,000
Total	15,279,000	3,341,000	10,251,000
Revenue Recognition
Percentage of revenue earned on a project basis	84.00%
Accounts Receivable
Period during which progress billings or contract price can be witheld until after completion of work	6 months
Retention	$ 48,000,000	$ 51,700,000
Warranty Costs
Labor warranty period after servicing of existing HVAC system	30 days
Revenue | Customer concentration | Maximum
Concentrations of Credit Risk
Single customer, percentage of revenue	3.00%