Retirement Plans (Tables)

12 Months Ended

Dec. 31, 2017

Defined Benefit Plan Disclosure [Line Items]

Summary of Asset Allocation

As of December 31, 2017 and 2016, these assets were allocated among asset categories as follows:

Asset Category	2017			2016			Current Minimum, Target and Maximum Allocation Policy
U.S. equity securities		51	%		51	%		30% — 50%— 70	%
International equity securities		21	%		19	%		0% — 20%— 30	%
Debt securities		28	%		30	%		15% — 30%— 55	%
Cash and cash equivalents		—	%		—	%		0% — 0%— 5	%
		100	%		100	%

Schedule of Change in Benefit Obligation

The following table presents the change in benefit obligation and plan assets for the Company’s defined benefit plans and postretirement benefit plan (in thousands):

															Other Postretirement Benefits
	Pension Benefits														Postretirement
	Pension Plan								SERP						Welfare Plan
	2017				2016				2017			2016			2017			2016
Change in benefit obligation
Benefit obligation at beginning of year		$	337,176			$	297,325		$	1,457		$	1,526		$	675		$	891
Service cost			10,677				13,402			—			—			—			—
Interest cost			13,729				14,123			58			65			27			29
Actuarial loss (gain)			34,563				19,120			42			12			52			(198	)
Curtailments			(33,433	)			—			—			—			—			—
Gross benefits paid			(7,718	)			(6,794	)		(145	)		(146	)		(75	)		(47	)
Benefit obligation at end of year		$	354,994			$	337,176		$	1,412		$	1,457		$	679		$	675
Accumulated benefit obligation at end of year		$	324,904			$	272,591		$	1,412		$	1,457		$	679		$	675

Weighted-Average Assumption Used to Determine Benefit Obligation and Net Periodic Benefit Cost

Weighted-average assumption used to determine benefit obligation at end of year
Discount rate		3.7	%		4.2	%	3.7	%	4.2	%	3.7	%	4.2	%
Rate of compensation increase	Service-based table			Service- based table			—		—		—		—
Health care cost trend rate
Initial rate		—			—		—		—		7.0	%	7.0	%
Ultimate rate		—			—		—		—		5.0	%	5.0	%
Years to ultimate		—			—		—		—		2022		2021

Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rate

Effect of one-percentage-point change in assumed health care cost trend rate on postretirement obligation
Increase	$	—	$	—	$	—	$	—	$	75		$	74
Decrease		—		—		—		—		(65	)		(64	)

Summary of Change in Plan Assets

Change in plan assets
Fair value of plan assets at beginning of year	$	257,517		$	243,588		$	—		$	—		$	—		$	—
Actual return on plan assets		45,196			20,723			—			—			—			—
Employer contribution		—			—			145			146			75			47
Gross benefits paid		(7,718	)		(6,794	)		(145	)		(146	)		(75	)		(47	)
Fair value of plan assets at end of year	$	294,995		$	257,517		$	—		$	—		$	—		$	—

Summary of Funded Status at End of Year

The following table presents the funded status and amounts recognized in the Company’s consolidated balance sheet for the Company’s defined benefit plans and postretirement benefit plan at December 31, 2017 and 2016 (in thousands):

													Other Postretirement Benefits
	Pension Benefits												Postretirement Welfare Plan
	Pension Plan						SERP
	2017			2016			2017			2016			2017			2016
Funded status at end of year
Fair value of plan assets	$	294,995		$	257,517		$	—		$	—		$	—		$	—
Benefit obligations		(354,994	)		(337,176	)		(1,412	)		(1,457	)		(679	)		(675	)
Funded status and amount recognized at end of year	$	(59,999	)	$	(79,659	)	$	(1,412	)	$	(1,457	)	$	(679	)	$	(675	)

Amounts Recognized in the Consolidated Balance Sheets

Amounts recognized in the consolidated balance sheets
Noncurrent asset	$	—		$	—		$	—		$	—		$	—		$	—
Current liability		—			—			(159	)		(150	)		(54	)		(56	)
Long-term liability		(59,999	)		(79,659	)		(1,253	)		(1,307	)		(625	)		(619	)

Amounts Recognized in Accumulated Other Comprehensive Income

Amounts recognized in accumulated other comprehensive income
Net actuarial loss (gain)	$	57,387	$	87,658	$	508	$	494	$	(5,053	)	$	(5,773	)
Prior service cost (credit)		—		—		—		—		—			—
Accumulated other compensation income	$	57,387	$	87,658	$	508	$	494	$	(5,053	)	$	(5,773	)

Projected Benefit Obligation in Excess of Plan Assets

The projected benefit obligation and fair value of plan assets for pension plans with a projected benefit obligation in excess of plan assets at December 31, 2017 and 2016 were as follows (in thousands):

	Pension Benefits
	Pension Plan				SERP
	2017		2016		2017		2016
Projected benefit obligation in excess of plan assets
Projected benefit obligation at end of year	$	354,994	$	337,176	$	1,412	$	1,457
Fair value of plan assets at end of year		294,995		257,517		—		—

Accumulated Benefit Obligation in Excess of Plan Assets

The projected benefit obligation, accumulated benefit obligation and fair value of plan assets for pension plans with an accumulated benefit obligation in excess of plan assets at December 31, 2017 and 2016 were as follows (in thousands):

	Pension Benefits
	Pension Plan				SERP
	2017		2016		2017		2016
Accumulated benefit obligation in excess of plan assets
Projected benefit obligation at end of year	$	354,994	$	337,176	$	1,412	$	1,457
Accumulated benefit obligation at end of year		324,904		272,591		1,412		1,457
Fair value of plan assets at end of year		294,995		257,517		—		—

Schedule of Employer Contribution

The following tables presents the expected cash flows for the Company’s defined benefit plans and postretirement benefit plan at December 31, 2017 and 2016 (in thousands):

									Other Postretirement Benefits
	Pension Benefits								Postretirement
	Pension Plan				SERP				Welfare Plan
	2017		2016		2017		2016		2017		2016
Expected employer contributions
First year	$	—	$	—	$	162	$	153	$	48	$	50

Expected Benefit Payments

									Other Postretirement Benefits
	Pension Benefits								Postretirement
	Pension Plan				SERP				Welfare Plan
	2017		2016		2017		2016		2017		2016
Expected benefit payments (gross)
Year one	$	9,483	$	8,032	$	162	$	153	$	55	$	58
Year two		10,131		8,835		159		157		56		58
Year three		10,818		9,646		156		155		58		58
Year four		11,608		10,400		152		151		58		58
Year five		12,377		11,201		149		148		46		57
Next five years		75,717		70,419		462		514		214		199

Summary of Expected Federal Subsidy

									Other Postretirement Benefits
	Pension Benefits								Postretirement
	Pension Plan				SERP				Welfare Plan
	2017		2016		2017		2016		2017			2016
Expected federal subsidy
Year one	$	—	$	—	$	—	$	—	$	(7	)	$	(7	)
Year two		—		—		—		—		(6	)		(7	)
Year three		—		—		—		—		(6	)		(7	)
Year four		—		—		—		—		(6	)		(7	)
Year five		—		—		—		—		(7	)		(7	)
Next five years		—		—		—		—		(30	)		(33	)

Pension Benefits [Member]

Defined Benefit Plan Disclosure [Line Items]

Components of Net Periodic Benefit Cost

The components of net periodic benefit cost and other changes in plan assets and benefit obligations recognized in other comprehensive income for the Company’s defined benefit plans for the years ended December 31, 2017, 2016 and 2015 were as follows (in thousands):

	Pension Benefits
	Pension Plan									SERP
	2017			2016			2015			2017		2016		2015
Components of net periodic benefit cost
Service cost	$	10,677		$	13,402		$	14,683		$	—	$	—	$	—
Interest cost		13,729			14,123			13,302			58		65		64
Expected return on plan assets		(18,195	)		(16,805	)		(17,921	)		—		—		—
Amortization:
Actuarial loss		4,400			5,484			7,728			28		26		28
Prior service credit		—			—			—			—		—		—
Net periodic benefit cost		10,611			16,204			17,792			86		91		92

Other changes in plan assets and benefit obligations recognized in other comprehensive income
Current year actuarial loss (gain)		7,562			15,203			(19,127	)		42			12			(30	)
Recognition of actuarial loss		(37,833	)		(5,484	)		(7,728	)		(28	)		(26	)		(28	)
Recognition of prior service credit		—			—			—			—			—			—
Total recognized in other comprehensive income		(30,271	)		9,719			(26,855	)		14			(14	)		(58	)
Total recognized in net periodic benefit cost and other comprehensive income	$	(19,660	)	$	25,923		$	(9,063	)	$	100		$	77		$	34

Weighted-Average Assumption Used to Determine Benefit Obligation and Net Periodic Benefit Cost

Weighted average assumptions used to determine net periodic benefit cost
Discount rate (1)		4.2/4.0	%		4.5	%	4.1	%	4.2	%	4.5	%	4.1	%
Expected long-term rate of return on plan assets		7.0	%		7.0	%	7.5	%	—		—		—
Rate of compensation increase	Service- based table			Service- based table			4.25	%	—		—		—

Estimated Amounts that will be Amortized from Accumulated Other Comprehensive Income into Net Periodic Benefit Cost

The estimated amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost in 2018 are as follows (in thousands):

	Pension Benefits
	Pension Plan		SERP
Actuarial loss	$	2,820	$	23
Prior service credit		—		—
	$	2,820	$	23

Other Postretirement Benefits [Member]

Defined Benefit Plan Disclosure [Line Items]

Components of Net Periodic Benefit Cost

The components of net periodic benefit cost and other changes in benefit obligations recognized in other comprehensive income for the Company’s postretirement benefit plan for the years ended December 31, 2017, 2016 and 2015 were as follows (in thousands):

	Other Postretirement Benefits
	Postretirement Welfare Plan
	2017			2016			2015
Components of net periodic benefit cost
Service cost	$	—		$	—		$	—
Interest cost		27			29			36
Amortization:
Actuarial gain		(668	)		(747	)		(793	)
Prior service cost		—			—			—
Net periodic benefit cost		(641	)		(718	)		(757	)

Other changes in benefit obligations recognized in other comprehensive income
Current year actuarial gain		52		(198	)		(322	)
Recognition of actuarial gain		668		747			793
Recognition of prior service cost		—		—			—
Adjustment for actual Medicare Part D reimbursement		—		(3	)		(3	)
Total recognized in other comprehensive income		720		546			468
Total recognized in net periodic benefit cost and other comprehensive income	$	79	$	(172	)	$	(289	)

Weighted-Average Assumption Used to Determine Benefit Obligation and Net Periodic Benefit Cost

Weighted average assumptions used to determine net periodic benefit cost
Discount rate	4.2	%	4.5	%	4.1	%
Health care cost trend rate:
Initial rate	7.0	%	6.5	%	7.0	%
Ultimate rate	5.0	%	5.0	%	5.0	%
Years to ultimate	2021		2019		2019

Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rate

Effect of one-percentage-point change in assumed health care cost trend rate on aggregate service and interest cost
Increase	$	3		$	4		$	5
Decrease		(3	)		(3	)		(4	)

Estimated Amounts that will be Amortized from Accumulated Other Comprehensive Income into Net Periodic Benefit Cost

The estimated amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost in 2018 are as follows (in thousands):

	Other Postretirement Benefits
	Postretirement Welfare Plan
Actuarial gain	$	(596	)
Prior service cost		—
	$	(596	)