Goodwill and Identifiable Intangible Assets, Net - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Changes in the carrying amount of goodwill
Balance at beginning of year	$ 464,392	$ 332,447
Acquisitions and purchase price adjustments (See Note 5)	127,722	131,945
Balance at end of period	592,114	464,392
Mechanical Services Segment
Changes in the carrying amount of goodwill
Balance at beginning of year	307,448	234,660
Acquisitions and purchase price adjustments (See Note 5)	52,771	72,788
Impact of segment reorganization	1,101
Balance at end of period	361,320	307,448
Accumulated impairment charges	116,600	116,600
Electrical Services Industry
Changes in the carrying amount of goodwill
Balance at beginning of year	156,944	97,787
Acquisitions and purchase price adjustments (See Note 5)	74,951	59,157
Impact of segment reorganization	(1,101)
Balance at end of period	$ 230,794	$ 156,944