Goodwill and Identifiable Intangible Assets, Net - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2020	Dec. 31, 2019
Changes in the carrying amount of goodwill
Balance at beginning of year	$ 332,447	$ 235,182
Acquisitions and purchase price adjustments (See Note 4)	88,335	97,265
Balance at end of period	420,782	332,447
Mechanical Services Segment
Changes in the carrying amount of goodwill
Balance at beginning of year	234,660	235,182
Acquisitions and purchase price adjustments (See Note 4)	73,409	579
Impact of segment reorganization		(1,101)
Balance at end of period	308,069	234,660
Electrical Services
Changes in the carrying amount of goodwill
Balance at beginning of year	97,787
Acquisitions and purchase price adjustments (See Note 4)	14,926	96,686
Impact of segment reorganization		1,101
Balance at end of period	$ 112,713	$ 97,787

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of increase (decrease), classified as other, of an asset representing the future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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