Employee Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Pension Plan [Member]
Change in benefit obligations:
Beginning projected benefit obligation	$ 58.1	$ 48.0
Service cost	1.7	1.5	1.4
Interest cost	2.7	2.6	2.4
Actuarial (gain)/loss	2.6	7.2
Benefits paid	(1.3)	(1.2)
Ending projected benefit obligation	63.8	58.1	48.0
Change in plan assets:
Beginning fair value	34.5	35.8
Actual return	4.3	(1.5)
Company contribution	1.7	1.5
Benefits paid	(1.4)	(1.3)
Ending fair value	39.1	34.5	35.8
Funded status of the plan	(24.7)	(23.6)
Supplementary Pension Plan [Member]
Change in benefit obligations:
Beginning projected benefit obligation	11.6	9.2
Service cost	0.3	0.2	0.3
Interest cost	0.5	0.5	0.5
Actuarial (gain)/loss	1.2	2.0
Benefits paid	(0.4)	(0.3)
Ending projected benefit obligation	13.2	11.6	9.2
Change in plan assets:
Beginning fair value	0	0
Actual return		0
Company contribution	0.4	0.4
Benefits paid	(0.4)	(0.4)
Ending fair value	0	0	0
Funded status of the plan	$ (13.2)	$ (11.6)