Employee Benefits (Schedule of Fair Value of Qualified Pension Plan Assets) (Details) - Qualified Pension Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	100.00%	100.00%
Fair value of plan assets	$ 87,364	$ 75,787	$ 65,710
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	65,355	54,361
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22,009	21,426
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	65.70%	63.80%
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	30.00%	32.40%
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	4.30%	3.80%
Fair value of plan assets	$ 3,760	$ 2,880
Cash and Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,760	2,880
Cash and Cash Equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and Cash Equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Obligations of U.S Government Agencies and U.S. Government-Sponsored Enterprises [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,926	4,233
Obligations of U.S Government Agencies and U.S. Government-Sponsored Enterprises [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Obligations of U.S Government Agencies and U.S. Government-Sponsored Enterprises [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,926	4,233
Obligations of U.S Government Agencies and U.S. Government-Sponsored Enterprises [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Obligations of states and political subdivisions [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,971	3,418
Obligations of states and political subdivisions [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Obligations of states and political subdivisions [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,971	3,418
Obligations of states and political subdivisions [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13,112	13,775
Corporate bonds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate bonds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13,112	13,775
Corporate bonds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	38,508	33,893
Common Stocks [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	38,508	33,893
Common Stocks [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common Stocks [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23,087	17,588
Mutual Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23,087	17,588
Mutual Funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Mutual Funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0