Fair Value (Reconciliation of all Assets Measured at Fair Value on Recurring Basis, Using Significant Unobservable Inputs (Level 3) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Obligations of State and Political Subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total Gains or Losses Included in Other Comprehensive Income	$ (18)	$ 17
Fair Value, Measurements, Recurring | Obligations of State and Political Subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance of Recurring Level 3 Assets at January 1	5,649	7,566
Total Gains or Losses Included in Other Comprehensive Income	(18)	17
Maturities / Calls	(460)	(865)
Purchases	0	0
Balance of Recurring Level 3 Assets at March 31	5,171	6,718
Fair Value, Measurements, Recurring | Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance of Recurring Level 3 Assets at January 1	353	353
Total Gains or Losses Included in Other Comprehensive Income	0	0
Maturities / Calls	0	0
Purchases	0	0
Balance of Recurring Level 3 Assets at March 31	$ 353	$ 353