Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	$ 5,910,038	$ 5,921,487
Gross unrealized gain	240,958	200,443
Gross unrealized loss	(55,370)	(99,457)
Fixed maturity securities - available for sale	6,095,626	6,022,473
Available for sale equity securities
Available-for-sale Equity Securities, Amortized Cost Basis	391,779	464,388
Gross unrealized gain	41,779	58,842
Gross unrealized loss	(7,469)	(5,764)
Available-for-sale Securities, Equity Securities	426,089	517,466
US Government and Government Agency Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	90,628	91,047
Gross unrealized gain	1,869	2,157
Gross unrealized loss	(400)	(495)
Fixed maturity securities - available for sale	92,097	92,709
Fixed Maturity Securities of States, Municipalities and Political Subdivisions Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	934,057	941,580
Gross unrealized gain	57,121	50,885
Gross unrealized loss	(2,361)	(5,979)
Fixed maturity securities - available for sale	988,817	986,486
Special Purpose Revenue Bonds Of States Municipalities And Political Subdivisions [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	2,242,766	2,240,412
Gross unrealized gain	98,757	71,541
Gross unrealized loss	(20,207)	(46,758)
Fixed maturity securities - available for sale	2,321,316	2,265,195
Corporate Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	1,172,614	1,195,387
Gross unrealized gain	45,490	40,860
Gross unrealized loss	(6,917)	(11,009)
Fixed maturity securities - available for sale	1,211,187	1,225,238
Residential Mortgage Backed Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	636,192	622,766
Gross unrealized gain	15,990	15,289
Gross unrealized loss	(14,893)	(19,936)
Fixed maturity securities - available for sale	637,289	618,119
Commercial Mortgage Backed Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	507,570	502,069
Gross unrealized gain	17,770	16,155
Gross unrealized loss	(8,808)	(13,336)
Fixed maturity securities - available for sale	516,532	504,888
Asset-backed Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	235,420	183,660
Gross unrealized gain	419	319
Gross unrealized loss	(1,576)	(1,587)
Fixed maturity securities - available for sale	234,263	182,392
Foreign Government Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	90,791	144,566
Gross unrealized gain	3,542	3,237
Gross unrealized loss	(208)	(357)
Fixed maturity securities - available for sale	$ 94,125	$ 147,446