Employee Benefits (Defined benefit and postretirement benefit plans) (Details 2)	12 Months Ended
	Dec. 31, 2019 USD ($) plan Y	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Pension Benefits
Employee benefits
Number of defined benefit plans | plan	2
Reconciliation of changes in benefit obligations
Benefit Obligation at Beginning of Year	$ 102,662,000	$ 110,080,000
Service Cost	0	0	$ 0
Interest Cost	4,401,000	4,193,000	4,665,000
Plan Amendment	0	0
Actuarial Losses (Gains)	(10,359,000)	5,031,000
Employer Benefits Paid	6,785,000	6,580,000
Benefit Obligation at End of Year	110,637,000	102,662,000	110,080,000
Reconciliation of changes in fair value of plan assets
Fair Value of Plan Assets at Beginning of Year	85,553,000	96,908,000
Actual Return on Plan Assets	14,400,000	(5,246,000)
Employer Contributions	470,000	471,000
Employer Benefits Paid	6,785,000	6,580,000
Fair Value of Plan Assets at End of Year	93,638,000	85,553,000	96,908,000
Funded Status at End of Year	(16,999,000)	(17,109,000)
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Net of Tax
Net Actuarial Gains (Losses)	41,404,000	42,127,000
Prior Service Credit	0	0
Total Amounts Recognized in Accumulated Other Comprehensive Income, Net of Tax	(41,404,000)	$ (42,127,000)
Pension Benefits | Excess retirement Plan
Employee benefits
Accumulated benefit obligation	$ 3,600,000
Postretirement Benefits
Employee benefits
Health Care Cost Trend Rate Assumed, Next Fiscal Year	5.70%	6.00%
Retirees' age and above which Medicare supplemental plan subsidy is provided (in years) | Y	65
Limit on annual credit provided in HRA to eligible employees	$ 1,200
Reconciliation of changes in benefit obligations
Benefit Obligation at Beginning of Year	23,452,000	$ 24,206,000
Service Cost	455,000	457,000	453,000
Interest Cost	1,025,000	936,000	1,093,000
Plan Amendment	0	0
Actuarial Losses (Gains)	(4,095,000)	869,000
Employer Benefits Paid	1,456,000	1,278,000
Benefit Obligation at End of Year	27,571,000	23,452,000	24,206,000
Reconciliation of changes in fair value of plan assets
Fair Value of Plan Assets at Beginning of Year	0	0
Actual Return on Plan Assets	0	0
Employer Contributions	1,456,000	1,278,000
Employer Benefits Paid	1,456,000	1,278,000
Fair Value of Plan Assets at End of Year	0	0	$ 0
Funded Status at End of Year	(27,571,000)	(23,452,000)
Participants contributions	700,000	600,000
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Net of Tax
Net Actuarial Gains (Losses)	(1,003,000)	(4,261,000)
Prior Service Credit	1,645,000	1,856,000
Total Amounts Recognized in Accumulated Other Comprehensive Income, Net of Tax	2,648,000	6,117,000
Other Pension Plan [Member]
Reconciliation of changes in benefit obligations
Actuarial Losses (Gains)	(10,800,000)	5,400,000
Postemployment Retirement Benefits [Member]
Reconciliation of changes in benefit obligations
Actuarial Losses (Gains)	$ (3,400,000)	$ 1,600,000