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Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
Segment Information (Details) $ in Thousands	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Information
Number of reportable segments \| segment									2
Revenue	$ 719,584	$ 706,918	$ 650,302	$ 538,473	$ 588,359	$ 594,536	$ 535,043	$ 464,941	$ 2,615,277	$ 2,182,879	$ 1,787,922
Gross Profit	132,560	$ 142,702	$ 120,016	$ 106,665	118,175	$ 127,868	$ 111,183	$ 89,053	501,943	446,279	366,281
Capital Expenditures									31,750	27,268	35,467
Total Assets	1,505,012				1,062,564				1,505,012	1,062,564
Operating \| Mechanical Services
Segment Information
Revenue									2,251,560	2,176,223	1,787,922
Gross Profit									465,144	444,960	366,281
Capital Expenditures									27,933	25,945	34,587
Total Assets	1,056,609				970,995				1,056,609	970,995
Operating \| Electrical Services
Segment Information
Revenue									363,717	6,656
Gross Profit									36,799	1,319
Capital Expenditures									1,504	57
Total Assets	372,254				23,078				372,254	23,078
Corporate & Eliminations
Segment Information
Capital Expenditures									2,314	1,266	$ 880
Total Assets	$ 76,149				$ 68,491				$ 76,149	$ 68,491