Investments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	$ 6,078,453	$ 5,921,487
Gross unrealized gain	281,520	200,443
Gross unrealized loss	(26,782)	(99,457)
Fixed maturity securities - available for sale	6,333,191	6,022,473
Available for sale equity securities
Available-for-sale Equity Securities, Amortized Cost Basis	394,685	464,388
Gross unrealized gain	59,130	58,842
Gross unrealized loss	(5,130)	(5,764)
Available-for-sale Securities, Equity Securities	448,685	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	84,479	91,047
Gross unrealized gain	1,354	2,157
Gross unrealized loss	(206)	(495)
Fixed maturity securities - available for sale	85,627	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	905,732	941,580
Gross unrealized gain	60,882	50,885
Gross unrealized loss	(909)	(5,979)
Fixed maturity securities - available for sale	965,705	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	2,263,181	2,240,412
Gross unrealized gain	121,364	71,541
Gross unrealized loss	(7,582)	(46,758)
Fixed maturity securities - available for sale	2,376,963	2,265,195
Corporate Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	1,151,993	1,195,387
Gross unrealized gain	51,846	40,860
Gross unrealized loss	(4,128)	(11,009)
Fixed maturity securities - available for sale	1,199,711	1,225,238
Residential Mortgage Backed Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	753,516	622,766
Gross unrealized gain	19,881	15,289
Gross unrealized loss	(8,863)	(19,936)
Fixed maturity securities - available for sale	764,534	618,119
Commercial Mortgage Backed Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	530,075	502,069
Gross unrealized gain	20,941	16,155
Gross unrealized loss	(3,899)	(13,336)
Fixed maturity securities - available for sale	547,117	504,888
Asset-backed Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	304,866	183,660
Gross unrealized gain	622	319
Gross unrealized loss	(1,092)	(1,587)
Fixed maturity securities - available for sale	304,396	182,392
Foreign Government Securities [Member]
Fixed Maturity & Equity Securities Available for Sale
Available-for-sale Fixed Maturity Securities, Amortized Cost Basis	84,611	144,566
Gross unrealized gain	4,630	3,237
Gross unrealized loss	(103)	(357)
Fixed maturity securities - available for sale	$ 89,138	$ 147,446