Accumulated Other Comprehensive Income (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Accumulated other comprehensive income		$ (108,781,000)	$ 42,070,000	$ (108,781,000)	$ 42,070,000	$ 14,108,000	$ 10,975,000
Other Comprehensive Income Before Reclassifications				(124,027,000)	53,028,000
Reclassified from Accumulated Oher Comprehensive Income				693,000	(2,875,000)
Other Comprehensive Income (Loss), before Tax				(123,334,000)	50,153,000
Other Comprehensive Income (Loss), Tax				30,833,000	(19,058,000)
Other comprehensive income (loss), net of tax		(19,218,000)	11,658,000	(92,501,000)	31,095,000
Reclassification Where Impairment Was Not Previously Recognized				0	0
Unrealized Gain Loss on Securities OTTI [Member]
Accumulated other comprehensive income	[1]	4,060,000	3,170,000	4,060,000	3,170,000	3,411,000	2,975,000
Other Comprehensive Income Before Reclassifications	[1]			(173,000)	(44,000)
Reclassified from Accumulated Oher Comprehensive Income	[1]			68,000	320,000
Other Comprehensive Income (Loss), before Tax	[1]			(105,000)	276,000
Other Comprehensive Income (Loss), Tax	[1]			27,000	(105,000)
Other comprehensive income (loss), net of tax	[1]			(78,000)	171,000
Reclassification Where Impairment Was Not Previously Recognized				12,000	24,000
Unrealized Gain Loss on Securities Other [Member]
Accumulated other comprehensive income	[1]	(89,857,000)	57,547,000	(89,857,000)	57,547,000	30,326,000	27,328,000
Other Comprehensive Income Before Reclassifications	[1]			(123,854,000)	53,072,000
Reclassified from Accumulated Oher Comprehensive Income	[1]			(424,000)	(4,293,000)
Other Comprehensive Income (Loss), before Tax	[1]			(124,278,000)	48,779,000
Other Comprehensive Income (Loss), Tax	[1]			31,068,000	(18,536,000)
Other comprehensive income (loss), net of tax	[1]			(93,210,000)	30,243,000
Reclassification Where Impairment Was Not Previously Recognized				(12,000)	(24,000)
Pension Loss [Member]
Accumulated other comprehensive income	[2]	$ (22,984,000)	$ (18,647,000)	(22,984,000)	(18,647,000)	$ (19,629,000)	$ (19,328,000)
Other Comprehensive Income Before Reclassifications	[2]			0	0
Reclassified from Accumulated Oher Comprehensive Income	[2]			1,049,000	1,098,000
Other Comprehensive Income (Loss), before Tax	[2]			1,049,000	1,098,000
Other Comprehensive Income (Loss), Tax	[2]			(262,000)	(417,000)
Other comprehensive income (loss), net of tax	[2]			787,000	681,000
Reclassification Where Impairment Was Not Previously Recognized				0	$ 0
Accounting Standards Update 2018-02 Member [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				2,932,000
Accounting Standards Update 2018-02 Member [Member] | Unrealized Gain Loss on Securities OTTI [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				715,000
Accounting Standards Update 2018-02 Member [Member] | Unrealized Gain Loss on Securities Other [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				6,359,000
Accounting Standards Update 2018-02 Member [Member] | Pension Loss [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				(4,142,000)
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				(33,320,000)
Accounting Standards Update 2016-01 [Member] | Unrealized Gain Loss on Securities OTTI [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				0
Accounting Standards Update 2016-01 [Member] | Unrealized Gain Loss on Securities Other [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				(33,320,000)
Accounting Standards Update 2016-01 [Member] | Pension Loss [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification				$ 0

[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 requirement to revalue deferred tax assets and liabilities in the period of enactment stranded the effects of the tax rate change, mandated by the Tax Cuts and Jobs Act, in accumulated other comprehensive income. In response, the FASB issued ASU 2018-02, “Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income”, which the Company adopted on January 1, 2018. This ASU allowed the reclassification of the stranded tax effects from accumulated other comprehensive income (as shown in the table above) to retained earnings.As mentioned in Note 3, additional new accounting guidance, which was effective January 1, 2018, required the reclassification of unrealized gains on equity securities from accumulated other comprehensive income to retained earnings (also shown above).