Employee Benefits (Tables)

9 Months Ended

Sep. 30, 2018

Retirement Benefits [Abstract]

Schedule of Net Benefit Costs [Table Text Block]

The following table sets forth the Company's net periodic benefit costs related to its Pension Plan, SERP and Medical Plan:

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2018			2017			2018			2017
Pension Plan and SERP benefits	(in millions)
Service cost	$	0.2		$	0.2		$	0.6		$	0.6
Interest cost	1.2			1.2			3.4			3.6
Expected return on plan assets	(1.4		)	(1.3		)	(4.3		)	(4.0		)
Amortization of prior service costs(1)	0.2			0.3			0.6			0.9
Amortization of actuarial losses(1)	—			0.1			0.6			0.3
Curtailment loss(2)	0.3			0.7			0.3			0.7
Periodic expense	$	0.5		$	1.2		$	1.2		$	2.1
Medical Plan benefits
Interest cost	$	—		$	—		$	0.1		$	0.1
Amortization of prior service costs(1)	(0.1		)	(0.1		)	(0.2		)	(0.2		)
Periodic expense	$	(0.1	)	$	(0.1	)	$	(0.1	)	$	(0.1	)

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⁽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 when there is a significant reduction in, or an elimination of, defined benefit accruals for current employees' future services. These expenses relate to the Uinta Basin Divestiture for the three and nine months endedSeptember 30, 2018 and the Pinedale Divestiture for the three and nine months endedSeptember 30, 2017. The Uinta Basin Divestiture curtailment is recognized on the Condensed Consolidated Statements of Operations within "Interest and other income (expense)" for the three and nine months endedSeptember 30, 2018. The Pinedale Divestiture curtailment is recognized on the Condensed Consolidated Statements of Operations within "Net gain (loss) from asset sales, inclusive of severance costs" for the three and nine months endedSeptember 30, 2017.