Goodwill and Intangible Assets - Goodwill Rollforward (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Goodwill
Beginning Balance, Goodwill	$ 520.7	$ 520.7	$ 459.7
Reallocation		0.0
Foreign currency translation adjustments and other		(1.7)	(1.6)
Goodwill acquired during the year		287.5	67.9
Purchase price adjustment, goodwill		38.4	(5.3)
Ending Balance, Goodwill		844.9	520.7
Goodwill Impaired
Beginning Balance, accumulated goodwill impairment loss	147.1	147.1
Ending Balance, accumulated goodwill impairment loss		147.1	147.1
Skaff
Goodwill
Purchase price adjustment, goodwill	0.8	0.8
D&S East
Goodwill
Beginning Balance, Goodwill	73.6	73.6	37.3
Reallocation		0.0
Foreign currency translation adjustments and other		(0.9)	0.2
Goodwill acquired during the year		0.0	36.1
Purchase price adjustment, goodwill		44.3	0.0
Ending Balance, Goodwill		117.0	73.6
Goodwill Impaired
Beginning Balance, accumulated goodwill impairment loss	0.0	0.0
Ending Balance, accumulated goodwill impairment loss		0.0	0.0
D&S West
Goodwill
Beginning Balance, Goodwill	151.3	151.3	147.3
Reallocation		0.0
Foreign currency translation adjustments and other		0.0	(0.7)
Goodwill acquired during the year		0.0	4.7
Purchase price adjustment, goodwill		0.8	0.0
Ending Balance, Goodwill		152.1	151.3
Goodwill Impaired
Beginning Balance, accumulated goodwill impairment loss	82.5	82.5
Ending Balance, accumulated goodwill impairment loss		82.5	82.5
E&C
Goodwill
Beginning Balance, Goodwill	295.8	295.8	275.1
Reallocation		(295.8)
Foreign currency translation adjustments and other		0.0	(1.1)
Goodwill acquired during the year		0.0	27.1
Purchase price adjustment, goodwill		0.0	(5.3)
Ending Balance, Goodwill		0.0	295.8
Goodwill Impaired
Beginning Balance, accumulated goodwill impairment loss	64.6	64.6
Ending Balance, accumulated goodwill impairment loss		0.0	64.6
E&C Cryogenics
Goodwill
Beginning Balance, Goodwill	0.0	0.0	0.0
Reallocation		183.5
Foreign currency translation adjustments and other		(0.6)	0.0
Goodwill acquired during the year		0.0	0.0
Purchase price adjustment, goodwill		(6.7)	0.0
Ending Balance, Goodwill		176.2	0.0
Goodwill Impaired
Beginning Balance, accumulated goodwill impairment loss	0.0	0.0
Ending Balance, accumulated goodwill impairment loss		40.9	0.0
E&C FinFans
Goodwill
Beginning Balance, Goodwill	0.0	0.0	0.0
Reallocation		112.3
Foreign currency translation adjustments and other		(0.2)	0.0
Goodwill acquired during the year		287.5	0.0
Purchase price adjustment, goodwill		0.0	0.0
Ending Balance, Goodwill		399.6	0.0
Goodwill Impaired
Beginning Balance, accumulated goodwill impairment loss	$ 0.0	0.0
Ending Balance, accumulated goodwill impairment loss		$ 23.7	$ 0.0