Shareholders' Equity (Summary Of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated other comprehensive income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (121,581)				$ (54,612)				$ (121,581)	$ (54,612)	$ (128,041)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax									(44,898)	48,422
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax									(76)	(331)
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax									5,356	374
Other Comprehensive Income (Loss), Tax									(39,618)	48,465
Other comprehensive income (loss)									(66,969)	73,429	64,060
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax									(65,136)	(10,729)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									(1,833)	84,158
Income Tax Expense (Benefit)									235,858	142,388	222,961
Net earnings (loss) applicable to common shareholders	124,990	$ 116,895	$ 90,647	$ 78,777	88,197	$ 84,238	$ (1,100)	$ 75,279	411,309	246,614	326,568
Reclassification of amortization of net actuarial gains losses pension and post retirement from AOCI, gross									(8,436)	(5,996)	(2,843)
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax									0	0	(50)
Reclassification of pension and postretirement from accumulated other comprehensive income, tax									(3,206)	(2,278)	(1,103)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated other comprehensive income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(92,417)				(18,369)				(92,417)	(18,369)	(91,921)
Other comprehensive income (loss)									(74,048)	73,552
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax									(73,985)	(12,471)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									(63)	86,023	(5,320)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated other comprehensive income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	1,639				1,546				1,639	1,546	2,226
Other comprehensive income (loss)									93	(680)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax									7,093	4,903
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									(7,000)	(5,583)
Net earnings (loss) applicable to common shareholders									7,000	5,583	1,605
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated other comprehensive income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (30,803)				$ (37,789)				(30,803)	(37,789)	(38,346)
Other comprehensive income (loss)									6,986	557
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax									1,756	(3,161)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									5,230	3,718	1,790
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated other comprehensive income [Line Items]
Accretion Of Securities With Noncredit Related Impairment Losses									0	0	(1,878)
Income Tax Expense (Benefit)									0	0	(10)
Net earnings (loss) applicable to common shareholders									0	0	(17)
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net									0	0	(27)
Increase (Decrease) in Deferred Income Taxes									0	0	767
Fixed income securities gain loss [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated other comprehensive income [Line Items]
Gain (Loss) on Investments, Excluding Other than Temporary Impairments									102	(138,735)	10,419
Income Tax Expense (Benefit)									39	(52,712)	3,971
Net earnings (loss) applicable to common shareholders									63	(86,023)	6,448
Interest Rate Contract [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated other comprehensive income [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax									11,290	9,004	2,594
Income Tax Expense (Benefit)									$ 4,290	$ 3,421	$ 989