Other Comprehensive Income (Loss) (Amounts Reclassified From Accumulated Other Comprehensive Income Into Income, By Component) (Details) - USD ($) $ in Thousands		3 Months Ended																								12 Months Ended
		Dec. 31, 2018	[1]	Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	[1]	Dec. 31, 2017	[1]	Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses recognized in net income																										$ 0	$ (7,589)	$ (18,355)
Net realized investment gains (losses), excluding other-than-temporary impairment losses																										(11,974)	47,174	66,711
Income (Loss) Before Income Taxes																										(7,855)	87,295	629,920
Income Taxes																										(122,498)	313,463	(169,477)
Underwriting, acquisition and insurance expenses																										(1,777,511)	(1,589,464)	(1,497,125)
Net income (loss)		$ (753,374)		$ 409,028		$ 279,587		$ (65,594)		$ 439,326		$ (261,035)		$ 151,427		$ 71,040		$ 132,703		$ 83,421		$ 80,673		$ 163,646		(130,353)	400,758	460,443
Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Unrealized Holding Gains On Available-For-Sale Securities [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses recognized in net income	[2]																									0	(7,589)	(18,355)
Net realized investment gains (losses), excluding other-than-temporary impairment losses	[2]																									(9,935)	41,957	64,345
Income (Loss) Before Income Taxes	[2]																									(9,935)	34,368	45,990
Income Taxes	[2]																									2,086	(10,072)	(12,462)
Net income (loss)	[2]																									(7,849)	24,296	33,528
Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Net Actuarial Pension Loss [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Income Taxes																										622	648	351
Underwriting, acquisition and insurance expenses																										(2,963)	(3,815)	(1,951)
Net income (loss)																										$ (2,341)	$ (3,167)	$ (1,600)

[1] Effective January 1, 2018, the Company adopted ASU No. 2016-01. As a result, the change in fair value of equity securities is no longer recognized in other comprehensive income; rather, all changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 1.

[2] Effective January 1, 2018, the Company adopted ASU No. 2016-01 and equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income, rather, changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. See note 1.