Employee Benefits Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plan and SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		$ 0.2	$ 0.3	$ 0.6	$ 0.9
Interest cost		1.2	1.3	3.6	3.9
Expected return on plan assets		(1.3)	(1.4)	(4.0)	(4.2)
Amortization of prior service costs	[1]	0.3	0.3	0.9	0.9
Amortization of actuarial losses	[1]	0.1	0.2	0.3	0.6
Curtailment loss	[2]	0.7	0.0	0.7	0.0
Periodic expense		1.2	0.7	2.1	2.1
Medical Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost		0.0	0.1	0.1	0.2
Amortization of prior service costs	[1]	(0.1)	0.0	(0.2)	0.1
Periodic expense		$ (0.1)	$ 0.1	$ (0.1)	$ 0.3

[1] Amortization of prior service costs and actuarial losses out of accumulated other comprehensive income are recognized on the Condensed Consolidated Statements of Operations within "Interest and other income (expense)".

[2] A curtailment is recognized immediately when there is a significant reduction in, or an elimination of, defined benefit accruals for current employees' future services. These expenses relate to the Pinedale Divestiture and are recognized on the Condensed Consolidated Statements of Operations within "Gain (loss) from asset sales" for the three and nine months ended September 30, 2017.