Summary of Significant Accounting Policies (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (21,074)	$ (21,808)	$ (19,982)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	422	530	108
Accumulated other comprehensive loss, tax effect	160	200	60
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(21,496)	(22,338)	(20,090)
Accumulated other comprehensive loss, tax effect	$ (7,809)	$ (8,120)	$ (13,750)