Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense									$ (12,834)	$ (12,017)	$ (9,528)
Net Income	$ 20,890	$ 14,593	$ 14,255	$ 12,472	$ 15,820	$ 13,064	$ 15,271	$ 15,067	62,210	59,222	46,529
Salaries and Employee Benefits									(68,112)	(63,885)	(51,306)
Total Reclassifications for the Period									3,224	959
Unrealized Gains and Losses on Available-for-Sale Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total Reclassifications for the Period									3,224	986
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total Reclassifications for the Period									3,224	959	535
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains and Losses on Available-for-Sale Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Gain (Loss) on Securities									4,081	1,248	706
Income Tax Expense									(857)	(262)	(148)
Net Income									3,224	986	558
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Post Retirement Plan Items Actuarial Gains (Losses) | Postretirement Medical and Life Benefit Plan
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense									0	10	9
Net Income									0	(27)	(23)
Salaries and Employee Benefits									$ 0	$ (37)	$ (32)