Accumulated Other Comprehensive Income Balances Of Each Component Of Accumulated Other Comprehensive Income, Net Of Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance at January 1	$ 949	$ 15,945	$ 11,761
Cumulative-effect adjustment for adoption of new accounting standards		(13,627)
Other comprehensive income before reclassifications	2,151	(1,462)	4,968
Amounts reclassified from accumulated other comprehensive income	0	93	(784)
Net current-period other comprehensive income	2,151	(1,369)	4,184
Ending balance	3,100	949	15,945
Unrealized Gains and Losses On Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance at January 1	981	16,003	11,871
Cumulative-effect adjustment for adoption of new accounting standards		(13,616)
Other comprehensive income before reclassifications	2,151	(1,499)	4,922
Amounts reclassified from accumulated other comprehensive income	0	93	(790)
Net current-period other comprehensive income	2,151	(1,406)	4,132
Ending balance	3,132	981	16,003
Postretirement Benefits Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance at January 1	(32)	(58)	(110)
Cumulative-effect adjustment for adoption of new accounting standards		(11)
Other comprehensive income before reclassifications	0	37	46
Amounts reclassified from accumulated other comprehensive income	0	0	6
Net current-period other comprehensive income	0	37	52
Ending balance	$ (32)	$ (32)	$ (58)