Derivative Instruments (Details) (Interest rate contracts, USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015 agreement	Dec. 31, 2014 agreement	Dec. 31, 2013 agreement
Interest rate contracts
Derivative instruments
Variable rate of debt	one-month LIBOR	one-month LIBOR
Borrowings at variable interest rates	$ 475.1	$ 468.5
Number of interest rate swap agreements	0	0
Number of interest rate swap agreements during the period			1
Notional amount outstanding			100.0
Fixed interest rate (as a percent)			2.10%
(Benefit) expense recorded to net finance costs	$ 0.1