Retirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Employees' Pension Plan [Member]
Net Periodic Benefit Cost [Line Items]
Service Cost	$ 376	$ 353
Interest Cost	420	394
Expected Return on Plan Assets	(826)	(808)
Amortization of Prior Service (Credit) Cost	(14)	(20)
Amortization of Net Loss	138	138
Net Periodic Benefit Cost	94	57
Contributions to Retirement Benefits Plans	0	0
Select Executive Retirement Plan [Member]
Net Periodic Benefit Cost [Line Items]
Service Cost	8	3
Interest Cost	58	48
Expected Return on Plan Assets	0	0
Amortization of Prior Service (Credit) Cost	14	15
Amortization of Net Loss	28	30
Net Periodic Benefit Cost	108	96
Contributions to Retirement Benefits Plans	107	115
Post-Retirement Benefit Plans [Member]
Net Periodic Benefit Cost [Line Items]
Service Cost	62	43
Interest Cost	80	58
Expected Return on Plan Assets	0	0
Amortization of Prior Service (Credit) Cost	(3)	(8)
Amortization of Net Loss	0	24
Net Periodic Benefit Cost	139	117
Contributions to Retirement Benefits Plans	$ 78	$ 47