Defined Benefit Pension Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Qualified Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 537	$ 537	$ 1,074	$ 1,074
Interest cost	667	644	1,336	1,288
Expected return on plan assets	(1,235)	(1,159)	(2,471)	(2,317)
Amortization of prior service (credit) cost	(5)	(5)	(11)	(11)
Recognized net actuarial loss	278	207	557	414
Net periodic benefit cost	242	224	485	448
Non-Qualified Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	33	31	65	61
Interest cost	107	108	214	216
Expected return on plan assets	0	0	0	0
Amortization of prior service (credit) cost	0	0	0	0
Recognized net actuarial loss	128	61	193	123
Net periodic benefit cost	$ 268	$ 200	$ 472	$ 400