Comprehensive Income (Loss) (Components Of Accumulated Other Comprehensive Income (Loss), Net Of Tax, In The Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Balance, beginning of period	$ 5,479,344	$ 5,065,880	$ 5,298,553	$ 4,958,310	$ 4,958,310
Current period change	7,724	56,031	19,267	117,818
Balance, end of period	5,522,794	$ 5,194,238	5,522,794	5,194,238	5,298,553
Ending balance of accumulated other comprehensive income (loss)	(17,048)		(17,048)		(36,315)
URA(D) On Securities [Member]
Balance, beginning of period			39,041	13,654	13,654
Current period change			8,800		22,063
Balance, end of period	45,361		45,361		39,041
URA(D) On Securities - OTTI [Member]
Current period change			(2,480)		3,324
Foreign Currency Translation Adjustments [Member]
Balance, beginning of period			(9,852)	(12,701)	(12,701)
Current period change			8,939		2,849
Balance, end of period	(913)		(913)		(9,852)
Benefit Plan Net Gain (Loss) [Member]
Balance, beginning of period			(65,504)	$ (63,089)	(63,089)
Current period change			4,008		(2,415)
Balance, end of period	$ (61,496)		$ (61,496)		$ (65,504)