Employee Benefit Plans - Net Periodic Pension Cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Pension Plan [Member]
Summary of net periodic pension cost [Abstract]
Service cost - benefits earned during the year	$ 1.7	$ 1.7	$ 1.5
Interest cost on accumulated benefit obligation	2.6	2.7	2.6
Expected return on plan assets	(2.9)	(2.6)	(2.9)
Net amortization and deferral	1.0	1.0	0.1
Net periodic pension cost	2.4	2.8	1.3
Supplementary Pension Plan [Member]
Summary of net periodic pension cost [Abstract]
Service cost - benefits earned during the year	0.4	0.3	0.2
Interest cost on accumulated benefit obligation	0.5	0.5	0.5
Expected return on plan assets	0	0	0
Net amortization and deferral	0.3	0.2	0.1
Net periodic pension cost	$ 1.2	$ 1.0	$ 0.8