Employee Benefit Plans (Components of Postretirement Benefit Expense) (Details) - Postretirement Medical and Life Benefit Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 110	$ 83	$ 69
Interest Cost	41	43	34
Amortization of Prior Service Costs	2	0	0
Amortization of Unrecognized Net (Gain) Loss	64	37	32
Net Postretirement Benefit Expense	217	163	135
Net Gain (Loss) During Period Recognized in Other Comprehensive Income (Loss)	15	273	41
Total Recognized in Net Postretirement Benefit Expense and Other Comprehensive Income	$ 232	$ 436	$ 176