Other Comprehensive Income (Loss) (Schedule of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Tax Expense									$ (12,017)	$ (9,528)	$ (11,534)
Net Income	$ 15,820	$ 13,064	$ 15,271	$ 15,067	$ 10,980	$ 12,639	$ 11,097	$ 11,813	59,222	46,529	40,676
Salaries and Employee Benefits									(63,885)	(51,306)	(46,642)
Total Reclassifications for the Period									959	535
Unrealized Gains and Losses on Available-for-Sale Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total Reclassifications for the Period									986	558
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total Reclassifications for the Period									959	535	382
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									1,248	706	596
Income Tax Expense									(262)	(148)	(209)
Net Income									986	558	387
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									10	9	3
Net Income									(27)	(23)	(5)
Salaries and Employee Benefits									$ (37)	$ (32)	$ (8)