Investments (Summary Of Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustment	$ 74,793	$ 76,459	$ 137,697	$ 135,569
Funds held interest income (expense)	978	974	2,917	3,628
Interest income from Parent	1,075	1,075	2,150	2,150
Gross investment income	76,846	78,508	142,764	141,347
Investment expenses	(4,946)	(4,636)	(10,015)	(9,030)
Net investment income	71,900	73,872	132,749	132,317
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustment	49,601	44,795	96,581	90,121
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustment	6,370	8,734	13,118	17,882
Short-Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustment	590	251	980	555
Limited Partnerships [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustment	8,978	14,192	8,754	11,678
Dividends From Preferred Shares Of Affiliate [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustment	7,758	7,758	15,516	15,516
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustment	$ 1,496	$ 729	$ 2,748	$ (183)