Employee Benefit Plans (Schedule of Benefits Plans) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Benefit Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost	$ 600	$ 577	$ 1,200	$ 1,154
Interest Cost	786	761	1,572	1,523
Expected Return on Assets	(1,122)	(1,004)	(2,245)	(2,007)
Amortization of Unrecognized Losses	391	357	783	713
Amortization of Unrecognized Prior Service Credit
Net Periodic Benefit Cost	655	691	1,310	1,383
Other Benefits Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost	272	275	544	550
Interest Cost	491	488	982	976
Expected Return on Assets	(601)	(558)	(1,203)	(1,116)
Amortization of Unrecognized Losses	445	443	890	886
Amortization of Unrecognized Prior Service Credit	(432)	(432)	(864)	(864)
Net Periodic Benefit Cost	$ 175	$ 216	$ 349	$ 432