Revenue - Disaggregation by Timing (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue
Sales to external customers	$ 290.1	$ 272.2	$ 277.9	$ 244.1	$ 269.4	$ 202.7	$ 199.8	$ 171.0	$ 1,084.3	$ 842.9	$ 722.0
Point in time
Disaggregation of Revenue
Sales to external customers									758.2
Over time
Disaggregation of Revenue
Sales to external customers									326.1
Operating Segments | Energy & Chemicals
Disaggregation of Revenue
Sales to external customers									390.5	225.6	154.3
Operating Segments | Energy & Chemicals | Point in time
Disaggregation of Revenue
Sales to external customers									136.2
Operating Segments | Energy & Chemicals | Over time
Disaggregation of Revenue
Sales to external customers									254.3
Operating Segments | D&S West
Disaggregation of Revenue
Sales to external customers									455.5	400.6	378.1
Operating Segments | D&S West | Point in time
Disaggregation of Revenue
Sales to external customers									405.3
Operating Segments | D&S West | Over time
Disaggregation of Revenue
Sales to external customers									50.2
Operating Segments | D&S East
Disaggregation of Revenue
Sales to external customers									246.3	232.3	197.6
Operating Segments | D&S East | Point in time
Disaggregation of Revenue
Sales to external customers									222.9
Operating Segments | D&S East | Over time
Disaggregation of Revenue
Sales to external customers									23.4
Intersegment Eliminations
Disaggregation of Revenue
Sales to external customers									(8.0)	$ (15.6)	$ (8.0)
Intersegment Eliminations | Point in time
Disaggregation of Revenue
Sales to external customers									(6.2)
Intersegment Eliminations | Over time
Disaggregation of Revenue
Sales to external customers									$ (1.8)