Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense	$ (11,606)	$ (12,069)	$ (11,464)
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total Reclassifications, Net of Tax	468	933	1,823
Unrealized Gains and Losses on Available-for-Sale Securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Gain (Loss) on Securities	725	1,481	2,429
Income Tax Expense	(254)	(518)	(850)
Total Reclassifications, Net of Tax	471	963	1,579
Defined Benefit Pension Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial Gains (Losses) Amortization	0	0	(749)
Defined Benefit Pension Plans | Amortization of Defined Benefit Pension Items | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior Service Costs Amortization	0	0	13
Actuarial Gains (Losses) Amortization	0	0	360
Income Tax Expense	0	0	(151)
Total Reclassifications, Net of Tax	0	0	222
Postretirement Medical and Life Benefit Plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial Gains (Losses) Amortization	22	96	(80)
Postretirement Medical and Life Benefit Plan | Amortization of Defined Benefit Pension Items | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial Gains (Losses) Amortization	(5)	(50)	37
Income Tax Expense	2	20	(15)
Total Reclassifications, Net of Tax	$ (3)	$ (30)	$ 22