Business Combinations Hetsco Acquisition (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Jan. 13, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 468.8			$ 218.0	$ 218.4
Hetsco [Member]
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired			100.00%
Goodwill	8.8	$ 10.1
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Goodwill	(1.3)
Customer relationships acquired	8.1	7.3
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles	0.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	1.2	1.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	4.7	4.6
Business Combination Provisional Information Initial Accounting Incomplete, other net assets	0.1
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	22.8	$ 23.2
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	$ (0.4)