Retirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Employees' Pension Plan
Net Periodic Benefit Cost [Line Items]
Service Cost	$ 350	$ 376	$ 700	$ 752
Interest Cost	373	424	723	844
Expected Return on Plan Assets	(800)	(828)	(1,600)	(1,656)
Amortization of Prior Service (Credit) Cost	(14)	(15)	(28)	(30)
Amortization of Net Loss	148	138	296	278
Net Periodic Benefit Cost	57	95	91	188
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	20	16
Interest Cost	59	48	109	106
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	14	14	28	29
Amortization of Net Loss	33	28	63	56
Net Periodic Benefit Cost	116	98	220	207
Plan Contributions During the Period	116	112	229	219
Estimated Future Contributions in the Current Fiscal Year			229
Post-Retirement Benefit Plans
Net Periodic Benefit Cost [Line Items]
Service Cost	37	63	74	125
Interest Cost	63	15	149	96
Expected Return on Plan Assets	0	0	0	0
Amortization of Prior Service (Credit) Cost	(3)	(3)	(6)	(6)
Amortization of Net Loss	0	0	0	0
Net Periodic Benefit Cost	97	75	217	215
Plan Contributions During the Period	$ 177	$ 72	230	$ 150
Estimated Future Contributions in the Current Fiscal Year			$ 230