Employee Benefits (Details 4) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effect of one-percentage-point change in assumed health care cost trend rates
Effect of 1% increase on total service and interest cost components	$ 0.1	$ 0.1
Effect of 1% decrease on total service and interest cost components	(0.1)	(0.1)
Effect of 1% increase on postretirement benefit obligation	0.4	0.5
Effect of 1% decrease on postretirement benefit obligation	(0.4)	(0.5)
Supplemental Executive Retirement Plans
Summary of benefit payments under the Company's various defined benefit plans, which reflect expected future employee service, as appropriate, expected to be paid in the future periods
2015	4.1
2016	1.3
2017	21.4
2018	1.2
2019	6.0
2020-2024	5.5
Amounts in accumulated other comprehensive loss that are expected to be recognized as components of net periodic benefit cost during 2015
Actuarial loss	1.5
Prior service (credit) cost	(0.3)
Total	1.2
Defined Benefit Plans
Summary of benefit payments under the Company's various defined benefit plans, which reflect expected future employee service, as appropriate, expected to be paid in the future periods
2015	3.6
2016	4.0
2017	4.1
2018	4.2
2019	4.6
2020-2024	26.9
Amounts in accumulated other comprehensive loss that are expected to be recognized as components of net periodic benefit cost during 2015
Actuarial loss	1.8
Prior service (credit) cost	0.2
Total	2.0
Postretirement Medical Plan
Employee Benefits
Number of subsidiaries of entity	1
Maximum age limit for eligibility	65 years
Summary of benefit payments under the Company's various defined benefit plans, which reflect expected future employee service, as appropriate, expected to be paid in the future periods
2015	0.8
2016	0.8
2017	1.0
2018	0.9
2019	1.1
2020-2024	5.2
Amounts in accumulated other comprehensive loss that are expected to be recognized as components of net periodic benefit cost during 2015
Actuarial loss	0.1
Prior service (credit) cost	(1.7)
Total	(1.6)
Supplemental Bonus Plan
General disclosures of the plan
Number of shares of the entity to be contributed to the plan as a result of acquisition	258,006
Number of shares equivalent to the cash liability associated with post-employment liability	95,980
Aggregate obligation to the plan acquired	5.9
(Income) expense from mark to market adjustments	$ (1.3)	$ 1.5	$ 1.6