Employee Benefits Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Plan and SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		$ 0.1	$ 0.2	$ 0.2	$ 0.6
Interest cost		1.2	1.2	3.6	3.4
Expected return on plan assets		(1.5)	(1.4)	(4.4)	(4.3)
Amortization of prior service costs(1)	[1]	0.0	0.2	0.2	0.6
Amortization of actuarial losses(1)	[1]	0.0	0.0	0.1	0.6
Curtailment (gain) loss(2)	[2]	0.0	0.3	0.4	0.3
Periodic expense		(0.2)	0.5	0.1	1.2
Medical Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost		0.0	0.0	0.1	0.1
Amortization of prior service costs(1)	[1]	0.0	(0.1)	0.0	(0.2)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment	[2]	0.0	0.0	(0.8)	0.0
Periodic expense		$ 0.0	$ (0.1)	$ (0.7)	$ (0.1)

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

[2] A curtailment is recognized when there is a significant reduction in, or an elimination of, defined benefit accruals for current employees' future services. The net curtailment gain between the SERP and Medical Plan of $0.4 million is related to the Haynesville Divestiture and corporate restructuring activities. Of the $0.4 million curtailment gain recognized, $0.2 million was recognized on the Condensed Consolidated Statements of Operations within "Interest and other income (expense)" and $0.2 million was recognized on the Condensed Consolidated Statements of Operations within "Net gain (loss) from asset sales, inclusive of restructuring costs" for the nine months ended September 30, 2019.