Accumulated Other Comprehensive Income (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Accumulated other comprehensive income (loss)		$ 343,435	$ 144,173	$ 343,435	$ 144,173	$ 110,444	$ (64,669)
Other Comprehensive Income Before Reclassifications				332,285	274,744
Reclassified from Accumulated Oher Comprehensive Income				(21,631)	3,710
Other Comprehensive Income (Loss), before Tax				310,654	278,454
Other Comprehensive Income (Loss), Tax				(77,663)	(69,612)
Other comprehensive income (loss), net of tax		(5,826)	35,275	232,991	208,842
Reclassification Where Impairment Was Not Previously Recognized				0	0
Cumulative Effect, Period of Adoption, Adjustment
Accumulated other comprehensive income (loss)						0
Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated other comprehensive income (loss)						110,444
Unrealized Gain Loss on Securities OTTI [Member]
Accumulated other comprehensive income (loss)	[1]	0	3,464	0	3,464	3,264	3,861
Other Comprehensive Income Before Reclassifications	[1]			0	(709)
Reclassified from Accumulated Oher Comprehensive Income	[1]			0	133
Other Comprehensive Income (Loss), before Tax	[1]			0	(576)
Other Comprehensive Income (Loss), Tax	[1]			0	144
Other comprehensive income (loss), net of tax	[1]			0	(432)
Reclassification Where Impairment Was Not Previously Recognized				0	35
Unrealized Gain Loss on Securities OTTI [Member] | Cumulative Effect, Period of Adoption, Adjustment
Accumulated other comprehensive income (loss)	[1]					(3,264)
Unrealized Gain Loss on Securities OTTI [Member] | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated other comprehensive income (loss)						0
Unrealized Gain Loss on Securities Other [Member]
Accumulated other comprehensive income (loss)	[1]	267,537	119,108	267,537	119,108	98,809	(52,278)
Other Comprehensive Income Before Reclassifications	[1]			237,583	229,288
Reclassified from Accumulated Oher Comprehensive Income	[1]			(16,965)	(728)
Other Comprehensive Income (Loss), before Tax	[1]			220,618	228,560
Other Comprehensive Income (Loss), Tax	[1]			(55,154)	(57,139)
Other comprehensive income (loss), net of tax	[1]			165,464	171,421
Reclassification Where Impairment Was Not Previously Recognized				0	(35)
Unrealized Gain Loss on Securities Other [Member] | Cumulative Effect, Period of Adoption, Adjustment
Accumulated other comprehensive income (loss)	[1]					3,264
Unrealized Gain Loss on Securities Other [Member] | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated other comprehensive income (loss)						102,073
Pension Loss [Member]
Accumulated other comprehensive income (loss)		(20,902)	(21,941)	(20,902)	(21,941)	(21,940)	(23,107)
Other Comprehensive Income Before Reclassifications				0	0
Reclassified from Accumulated Oher Comprehensive Income				1,384	1,554
Other Comprehensive Income (Loss), before Tax				1,384	1,554
Other Comprehensive Income (Loss), Tax				(346)	(388)
Other comprehensive income (loss), net of tax				1,038	1,166
Reclassification Where Impairment Was Not Previously Recognized				0	0
Pension Loss [Member] | Cumulative Effect, Period of Adoption, Adjustment
Accumulated other comprehensive income (loss)						0
Pension Loss [Member] | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated other comprehensive income (loss)						(21,940)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated other comprehensive income (loss)	[2]	$ 96,800	$ 43,542	96,800	43,542	30,311	$ 6,855
Other Comprehensive Income Before Reclassifications	[2]			94,702	46,165
Reclassified from Accumulated Oher Comprehensive Income	[2]			(6,050)	2,751
Other Comprehensive Income (Loss), before Tax	[2]			88,652	48,916
Other Comprehensive Income (Loss), Tax	[2]			(22,163)	(12,229)
Other comprehensive income (loss), net of tax	[2]			66,489	36,687
Reclassification Where Impairment Was Not Previously Recognized				$ 0	$ 0
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Cumulative Effect, Period of Adoption, Adjustment
Accumulated other comprehensive income (loss)	[2]					0
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Cumulative Effect, Period of Adoption, Adjusted Balance
Accumulated other comprehensive income (loss)						$ 30,311

[1] The pre-tax amounts reclassified from accumulated other comprehensive income to current earnings are included in "investment securities gains (losses), net" in the consolidated statements of income.

[2] The pre-tax amounts reclassified from accumulated other comprehensive income to current earnings are included in "interest and fees on loans" in the consolidated statements of income.