Investments (Securities in Unrealized Loss Position) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	$ 1,725,902	$ 806,757
Less than 12 months, Unrealized losses	(44,003)	(27,841)
12 months or more, Fair value	337,004	617,224
12 months or more, Unrealized losses	(19,143)	(13,935)
Total, Fair value	2,062,906	1,423,981
Total, Unrealized losses	(63,146)	(41,776)
US Government and Government Agency Securities [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	9,018	14,813
Less than 12 months, Unrealized losses	(53)	(8)
12 months or more, Fair value	3,985	11,236
12 months or more, Unrealized losses	(7)	(129)
Total, Fair value	13,003	26,049
Total, Unrealized losses	(60)	(137)
Fixed Maturity Securities of States, Municipalities and Political Subdivisions Securities [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	119,543	3,857
Less than 12 months, Unrealized losses	(2,173)	(21)
12 months or more, Fair value	0	19,337
12 months or more, Unrealized losses	0	(139)
Total, Fair value	119,543	23,194
Total, Unrealized losses	(2,173)	(160)
Special Purpose Revenue Bonds Of States Municipalities And Political Subdivisions [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	437,071	4,041
Less than 12 months, Unrealized losses	(6,738)	(19)
12 months or more, Fair value	18,348	100,947
12 months or more, Unrealized losses	(780)	(967)
Total, Fair value	455,419	104,988
Total, Unrealized losses	(7,518)	(986)
Corporate Securities [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	258,668	211,111
Less than 12 months, Unrealized losses	(4,594)	(2,498)
12 months or more, Fair value	40,654	48,091
12 months or more, Unrealized losses	(1,847)	(2,158)
Total, Fair value	299,322	259,202
Total, Unrealized losses	(6,441)	(4,656)
Residential Mortgage Backed Securities [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	271,212	37,434
Less than 12 months, Unrealized losses	(4,160)	(100)
12 months or more, Fair value	98,727	226,256
12 months or more, Unrealized losses	(3,203)	(3,879)
Total, Fair value	369,939	263,690
Total, Unrealized losses	(7,363)	(3,979)
Commercial Mortgage Backed Securities [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	107,636	5,228
Less than 12 months, Unrealized losses	(1,338)	(26)
12 months or more, Fair value	24,216	99,868
12 months or more, Unrealized losses	(936)	(2,006)
Total, Fair value	131,852	105,096
Total, Unrealized losses	(2,274)	(2,032)
Asset-backed Securities [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	150,415	181,579
Less than 12 months, Unrealized losses	(269)	(1,245)
12 months or more, Fair value	72,839	78,797
12 months or more, Unrealized losses	(587)	(1,347)
Total, Fair value	223,254	260,376
Total, Unrealized losses	(856)	(2,592)
Foreign Government Securities [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	30,582	55,280
Less than 12 months, Unrealized losses	(1,052)	(1,498)
12 months or more, Fair value	12,893	7,187
12 months or more, Unrealized losses	(432)	(56)
Total, Fair value	43,475	62,467
Total, Unrealized losses	(1,484)	(1,554)
Foreign Corporate Securities [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	171,921	182,163
Less than 12 months, Unrealized losses	(7,203)	(4,587)
12 months or more, Fair value	42,054	21,571
12 months or more, Unrealized losses	(5,383)	(2,306)
Total, Fair value	213,975	203,734
Total, Unrealized losses	(12,586)	(6,893)
Equity Securities [Member]
Gross unrealized losses and fair value of all available for sale securities that were in a continuous loss position
Less than 12 months, Fair value	169,836	111,251
Less than 12 months, Unrealized losses	(16,423)	(17,839)
12 months or more, Fair value	23,288	3,934
12 months or more, Unrealized losses	(5,968)	(948)
Total, Fair value	193,124	115,185
Total, Unrealized losses	$ (22,391)	$ (18,787)