Retirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Periodic Benefit Cost [Line Items]
Employer matching contribution, Percentage			5.00%
Employees' Pension Plan
Net Periodic Benefit Cost [Line Items]
Service Cost	$ 389	$ 350	$ 1,168	$ 1,050
Interest Cost	400	362	1,199	1,085
Expected Return on Plan Assets	(841)	(800)	(2,522)	(2,399)
Amortization of Prior Service (Credit) Cost	(12)	(14)	(37)	(43)
Amortization of Net Loss	48	148	145	443
Net Periodic (Benefit) Cost	(16)	46	(47)	136
Plan Contributions During the Period	0	0	0	0
Estimated Future Contributions in the Current Fiscal Year	0		0
Select Executive Retirement Plan
Net Periodic Benefit Cost [Line Items]
Service Cost	104	10	311	30
Interest Cost	48	55	152	164
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	14	14	43	43
Amortization of Net Loss	33	31	99	94
Net Periodic (Benefit) Cost	199	110	605	331
Plan Contributions During the Period	116	116	349	345
Estimated Future Contributions in the Current Fiscal Year	0		0
Post-Retirement Benefit Plans
Net Periodic Benefit Cost [Line Items]
Service Cost	34	37	102	110
Interest Cost	81	75	248	224
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	25	(3)	75	(8)
Amortization of Net Loss	0	0	0	0
Net Periodic (Benefit) Cost	140	109	425	326
Plan Contributions During the Period	56	$ 65	175	$ 295
Estimated Future Contributions in the Current Fiscal Year	$ 0		$ 0
On Or Subsequent to January 1, 2003
Net Periodic Benefit Cost [Line Items]
Service credits, percent of eligible salaries			6.00%
Minimum | Prior to January 1, 2003
Net Periodic Benefit Cost [Line Items]
Service credits, percent of eligible salaries			6.00%
Maximum | Prior to January 1, 2003
Net Periodic Benefit Cost [Line Items]
Service credits, percent of eligible salaries			12.00%