Retirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employees' Pension Plan
Net Periodic Benefit Cost [Line Items]
Service Cost	$ 350	$ 376	$ 1,050	$ 1,127
Interest Cost	362	420	1,085	1,262
Expected Return on Plan Assets	(800)	(828)	(2,399)	(2,483)
Amortization of Prior Service (Credit) Cost	(14)	(14)	(43)	(42)
Amortization of Net Loss	148	140	443	419
Net Periodic Benefit Cost	46	94	136	283
Plan Contributions During the Period	0	0	0	0
Estimated Future Contributions in the Current Fiscal Year			0
Select Executive Retirement Plan
Net Periodic Benefit Cost [Line Items]
Service Cost	10	8	30	24
Interest Cost	55	56	164	163
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	14	14	43	43
Amortization of Net Loss	31	28	94	84
Net Periodic Benefit Cost	110	106	331	314
Plan Contributions During the Period	116	131	345	350
Estimated Future Contributions in the Current Fiscal Year			115
Post-Retirement Benefit Plans
Net Periodic Benefit Cost [Line Items]
Service Cost	37	63	110	188
Interest Cost	75	83	224	178
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	(3)	(3)	(8)	(8)
Amortization of Net Loss	0	0	0	0
Net Periodic Benefit Cost	109	143	326	358
Plan Contributions During the Period	$ 65	$ 47	295	$ 197
Estimated Future Contributions in the Current Fiscal Year			$ 98