Goodwill - Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019	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)	14,944		97,265
Impairment adjustment		$ 0
Balance at end of period	347,391	332,447	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)			579
Impact of segment reorganization	(1,101)
Balance at end of period	234,660	234,660	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)	14,944		96,686
Impact of segment reorganization	1,101
Balance at end of period	$ 112,731	$ 97,787	$ 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 loss from the write-down of an asset representing the 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 (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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