Qualified Employee Benefit Plans - Actuarial Computations Used to Determine Net Periodic Costs (Details) - Retirement Plan [Member]	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assumptions used to determine net periodic benefit costs [Abstract]
Discount rate on benefit obligations	4.55%	4.75%	4.30%
Expected long-term rate of return on plan assets	6.00%	6.50%	7.00%

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Period Type:	duration