Benefit Plans - Development of Funded Status (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension and Supplemental Executive Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation	$ 375,562	$ 411,996
Projected Benefit Obligation	(376,153)	(417,770)	$ (369,808)
Plan Assets at Fair Value	359,719	401,142	360,900
Funded Status - Overfunded/(Underfunded)	(16,434)	(16,628)
Other Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation	28,085	24,716
Projected Benefit Obligation	(28,085)	(24,716)	(17,378)
Plan Assets at Fair Value	77,762	85,303	$ 70,408
Funded Status - Overfunded/(Underfunded)	$ 49,677	$ 60,587

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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- Definition

Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

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- Definition

Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919

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