Employee Benefits Schedule of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Plan and SERP [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost		$ 0.0	$ 0.2	$ 0.1	$ 0.4
Interest cost		1.2	1.1	2.4	2.2
Expected return on plan assets		(1.4)	(1.5)	(2.9)	(2.9)
Amortization of prior service costs(1)	[1]	0.1	0.2	0.2	0.4
Amortization of actuarial losses(1)	[1]	0.0	0.3	0.1	0.6
Curtailment (gain) loss(2)	[2]	0.1	0.0	0.4	0.0
Periodic expense		0.0	0.3	0.3	0.7
Medical Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost		0.1	0.1	0.1	0.1
Amortization of prior service costs(1)	[1]	0.0	0.0	0.0	(0.1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment	[2]	0.0	0.0	(0.8)	0.0
Periodic expense		$ 0.1	$ 0.1	$ (0.7)	$ 0.0

[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 six months ended June 30, 2019.