Investments (Summary Of Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustments	$ 90,014	$ 73,175
Funds held interest income (expense)	2,881	2,868
Interest income from Parent		1,075
Gross investment income	92,895	77,118
Investment expenses	(8,361)	(7,209)
Net investment income	84,534	69,909
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustments	67,054	42,419
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustments	1,431	4,403
Short-Term Investments and Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustments	2,736	928
Limited Partnerships [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustments	8,055	14,472
Dividends From Preferred Shares Of Affiliate [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustments	7,758	7,758
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross investment income before adjustments	$ 2,980	$ 3,195