Segment and Geographic Information - Segment income (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
Segment Reporting Information
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
Depreciation and amortization expense									50.8	37.6	33.1
Operating income (loss)	$ 26.3	$ 31.5	$ 19.3	$ 15.0	$ 20.9	$ 7.2	$ 8.5	$ 1.9	92.1	38.5	41.0
Capital expenditures									35.6	33.0	16.3
Intersegment Eliminations
Segment Reporting Information
Sales to external customers									(8.0)	(15.6)	(8.0)
Depreciation and amortization expense									0.0	0.0	0.0
Operating income (loss)									(2.5)	(3.6)	(2.1)
Capital expenditures									0.0	0.0	0.0
Corporate
Segment Reporting Information
Sales to external customers									0.0	0.0	0.0
Depreciation and amortization expense									1.5	2.2	3.1
Operating income (loss)									(51.4)	(62.4)	(46.1)
Capital expenditures									3.7	2.3	0.5
Energy & Chemicals | Operating Segments
Segment Reporting Information
Sales to external customers									390.5	225.6	154.3
Depreciation and amortization expense									27.0	15.3	10.0
Operating income (loss)									25.5	5.1	13.3
Capital expenditures									15.5	15.5	3.3
D&S West | Operating Segments
Segment Reporting Information
Sales to external customers									455.5	400.6	378.1
Depreciation and amortization expense									11.2	10.6	11.7
Operating income (loss)									101.2	85.2	75.6
Capital expenditures									6.0	4.1	3.9
D&S East | Operating Segments
Segment Reporting Information
Sales to external customers									246.3	232.3	197.6
Depreciation and amortization expense									11.1	9.5	8.3
Operating income (loss)									19.3	14.2	0.3
Capital expenditures									$ 10.4	$ 11.1	$ 8.6