Pension and Postretirement Benefit Plans - Actuarial Assumptions Used to Determine Benefit Obligations (Details)	Dec. 31, 2018	Dec. 31, 2017
SERP I and SERP II
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.95%	3.30%
PRBP
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.45%	2.75%

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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