Investments (Summary Of Amortized Cost And Market Value Of Fixed Maturity Securities, By Contractual Maturity) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	$ 5,862,000	$ 5,335,472
Fixed maturity securities - available for sale, at market value	6,014,941	5,356,477
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Due in one year or less, Amortized Cost	350,845	330,029
Fixed maturity securities - available for sale, Due after one year through five years, Amortized Cost	2,916,564	2,617,079
Fixed maturity securities - available for sale, Due after five years through ten years, Amortized Cost	803,666	870,266
Fixed maturity securities - available for sale, Due after ten years, Amortized Cost	796,811	595,783
Fixed maturity securities - available for sale, Due in one year or less, Market Value	349,366	330,509
Fixed maturity securities - available for sale, Due after one year through five years, Market Value	2,967,946	2,618,056
Fixed maturity securities - available for sale, Due after five years through ten years, Market Value	833,389	856,230
Fixed maturity securities - available for sale, Due after ten years, Market Value	860,168	631,806
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	167,721	145,755
Fixed maturity securities - available for sale, at market value	169,025	144,982
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	75,965	61,527
Fixed maturity securities - available for sale, at market value	77,497	62,446
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	750,339	714,907
Fixed maturity securities - available for sale, at market value	757,447	712,298
Non-agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities - available for sale, Amortized Cost	89	126
Fixed maturity securities - available for sale, at market value	$ 103	$ 150

Amount of debt securities categorized neither as held-to-maturity nor trading, held at market value.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the second fiscal year through the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing after the tenth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing after the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount after adjustments of available-for-sale debt securities at cost, maturing in the next fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings less cumulative-effect adjustments, and fair value hedge accounting adjustments. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Fair value of available-for-sale debt securities maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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