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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses recognized in net income													$ (44,481)	$ (4,784)	$ (4,706)
Net realized investment gains, excluding other-than-temporary impairment losses													150,961	50,784	67,858
Income Before Income Taxes													742,105	440,378	361,743
Underwriting, acquisition and insurance expenses													(1,455,080)	(1,460,882)	(1,312,312)
Income Taxes													(152,963)	(116,690)	(77,898)
Net Income	$ 198,273	$ 104,410	$ 92,453	$ 194,006	$ 118,222	$ 76,824	$ 41,141	$ 87,501	$ 98,939	$ 66,967	$ 28,676	$ 89,263	589,142	323,688	283,845
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													(44,481)	(4,784)	(4,706)
Net realized investment gains, excluding other-than-temporary impairment losses													154,230	40,835	61,918
Income Before Income Taxes													109,749	36,051	57,212
Income Taxes													(29,267)	(9,890)	(16,382)
Net Income													80,482	26,161	40,830
Reclassification Out Of Accumulated Other Comprehensive Income [Member] | Net Actuarial Pension Loss [Member]
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Underwriting, acquisition and insurance expenses													(2,662)	(2,084)	(1,934)
Income Taxes													532	318	386
Net Income													$ (2,130)	$ (1,766)	$ (1,548)