General - Fair Value of Identified Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 01, 2015	Jun. 30, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill at June 30, 2015		$ 294,492	$ 293,023
Schultz Mechanical Contractors, Inc. [Member]
Business Acquisition [Line Items]
Receivables and cost and estimated earnings in excess of billings	$ 1,100
Prepaid expenses and other current assets	19
Property, plant and equipment	162
Identified intangible assets	3,060
Accounts payable, accrued expenses and billings in excess of cost and estimated earnings	(461)
Total identifiable net assets	3,880
Total consideration recorded	7,878
Less: total identifiable net assets	$ 3,880
Goodwill at June 30, 2015		$ 3,998