Summary of Significant Accounting Policies (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (19,982)	$ (12,571)	$ (11,245)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	108	6,097	9,869
Accumulated other comprehensive (loss) income, tax effect	60	3,687	6,272
Accumulated Net Gain (Loss) from Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	0	0	(2)
Accumulated other comprehensive (loss) income, tax effect	0	0	0
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(20,090)	(18,668)	(21,112)
Accumulated other comprehensive (loss) income, tax effect	$ 13,750	$ 13,212	$ 14,491