Comprehensive Income (Loss) (Components Of Accumulated Other Comprehensive Income (Loss), Net Of Tax, In The Consolidated Balance Sheets) (Details) - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Comprehensive Income (Loss) [Line Items]
Beginning balance,		$ 5,044,665,000			$ 5,044,665,000
Change to beginning balance due to adoption of Accounting Standards Update 2016-01							$ 0	$ (2,447,000)
Current period change	$ 67,629,000		$ (37,008,000)		165,777,000	$ (88,192,000)
Ending balance,	5,743,746,000		5,047,046,000		5,743,746,000	5,047,046,000
URA(D) On Securities [Member]
Comprehensive Income (Loss) [Line Items]
Beginning balance,	31,483,000	(55,950,000)	(16,662,000)	$ 37,442,000	(55,950,000)	37,442,000
Change to beginning balance due to adoption of Accounting Standards Update 2016-01								(2,447,000)
Current period change	74,244,000		(18,221,000)		161,939,000	(69,956,000)
Ending balance,	105,436,000	31,483,000	(34,673,000)	(16,662,000)	105,436,000	(34,673,000)
URA(D) On Securities - OTTI [Member]
Comprehensive Income (Loss) [Line Items]
Current period change	(291,000)		210,000		(553,000)	288,000
Foreign Currency Translation Adjustments [Member]
Comprehensive Income (Loss) [Line Items]
Beginning balance,	6,678,000	(2,886,000)	32,203,000	33,545,000	(2,886,000)	33,545,000
Current period change	(7,475,000)		(20,812,000)		2,089,000	(22,154,000)
Ending balance,	(797,000)	6,678,000	11,391,000	32,203,000	(797,000)	11,391,000
Benefit Plan Net Gain (Loss) [Member]
Comprehensive Income (Loss) [Line Items]
Beginning balance,	(66,267,000)	(67,418,000)	(70,114,000)	(71,929,000)	(67,418,000)	(71,929,000)
Current period change	1,151,000		1,815,000		2,302,000	3,630,000
Ending balance,	(65,116,000)	(66,267,000)	(68,299,000)	(70,114,000)	(65,116,000)	(68,299,000)
Accumulated Other Comprehensive Income (Loss), Net Of Deferred Income Taxes [Member]
Comprehensive Income (Loss) [Line Items]
Beginning balance,	(28,106,000)	(126,254,000)	(54,573,000)	(942,000)	(126,254,000)	(942,000)
Change to beginning balance due to adoption of Accounting Standards Update 2016-01								$ (2,447,000)
Current period change	67,629,000	98,148,000	(37,008,000)	(51,184,000)
Ending balance,	$ 39,523,000	$ (28,106,000)	$ (91,581,000)	$ (54,573,000)	$ 39,523,000	$ (91,581,000)