Defined Benefit Pension Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 537	$ 537	$ 1,611	$ 1,611
Interest cost	669	644	2,005	1,932
Expected return on plan assets	(1,236)	(1,158)	(3,707)	(3,475)
Amortization of prior service (credit) cost	(6)	(6)	(17)	(17)
Recognized net actuarial loss	279	207	836	621
Net periodic benefit cost	243	224	728	672
Non-Qualified Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	32	30	97	91
Interest cost	107	108	321	324
Expected return on plan assets	0	0	0	0
Amortization of prior service (credit) cost	0	0	0	0
Recognized net actuarial loss	76	62	269	185
Net periodic benefit cost	$ 215	$ 200	$ 687	$ 600