Employee Benefits Schedule of Changes in Benefit Obligations and Fair Value of Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in plan assets
Fair value of plan assets at January 1,	$ 86.1
Fair value of plan assets at December 31,	100.5	$ 86.1
Pension Plan and SERP [Member]
Change in benefit obligation
Benefit obligation at January 1,	129.2	120.3
Service cost	0.8	1.2	$ 2.1
Interest cost	4.7	5.2	4.9
Curtailments	(0.3)	0.0
Benefit payments	(6.9)	(7.8)
Plan amendments	0.0	0.0
Actuarial loss (gain)	2.5	10.3
Benefit obligation at December 31,	130.0	129.2	120.3
Change in plan assets
Fair value of plan assets at January 1,	86.1	79.3
Actual return on plan assets	15.3	7.4
Company contributions to the plan	6.0	7.2
Benefit payments	(6.9)	(7.8)
Fair value of plan assets at December 31,	100.5	86.1	79.3
Underfunded status (current and long-term)	(29.5)	(43.1)
Amounts recognized in balance sheets
Accounts payable and accrued expenses	(1.5)	(2.5)
Other long-term liabilities	(27.9)	(40.6)
Total amount recognized in balance sheet	(29.4)	(43.1)
Amounts recognized in AOCI
Net actuarial loss (gain)	15.0	23.5
Prior service cost	1.2	2.9
Total amount recognized in AOCI	16.2	26.4
Medical Plan [Member]
Change in benefit obligation
Benefit obligation at January 1,	5.4	5.2
Service cost	0.0	0.0	0.0
Interest cost	0.1	0.2	0.2
Curtailments	0.0	0.0
Benefit payments	(0.1)	(0.4)
Plan amendments	(2.4)	0.0
Actuarial loss (gain)	(0.1)	0.4
Benefit obligation at December 31,	2.9	5.4	5.2
Change in plan assets
Fair value of plan assets at January 1,	0.0	0.0
Actual return on plan assets	0.0	0.0
Company contributions to the plan	0.1	0.4
Benefit payments	(0.1)	(0.4)
Fair value of plan assets at December 31,	0.0	0.0	$ 0.0
Underfunded status (current and long-term)	(2.9)	(5.4)
Amounts recognized in balance sheets
Accounts payable and accrued expenses	(0.2)	(0.3)
Other long-term liabilities	(2.6)	(5.1)
Total amount recognized in balance sheet	(2.8)	(5.4)
Amounts recognized in AOCI
Net actuarial loss (gain)	(0.5)	(0.4)
Prior service cost	(1.2)	1.0
Total amount recognized in AOCI	$ (1.7)	$ 0.6