Summary of significant accounting policies (Impairment of Long-Lived Assets) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Impairment charges	$ 0.3	$ 1.3	$ 1.1	$ 2.7
Impaired Long-Lived Assets Held and Used [Line Items]			$ 1.1