Employee Benefit Plans (Components of Postretirement Benefit Expense) (Details) - Postretirement Medical and Life Benefit Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 83	$ 69	$ 50
Interest Cost	43	34	29
Amortization of Unrecognized Net (Gain) Loss	37	32	8
Net Postretirement Benefit Expense	163	135	87
Net Gain (Loss) During Period Recognized in Other Comprehensive Income (Loss)	273	41	218
Total Recognized in Net Postretirement Benefit Expense and Other Comprehensive Income	$ 436	$ 176	$ 305