Investments (Gross Unrealized Losses on Investments, By Category and Length of Time) (Details) (Fixed Maturity Securities [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	$ 2,340,660	$ 2,346,226
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(57,680)	(56,929)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	486,894	2,731,950
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(52,022)	(98,492)
Available for sale securities, continuous unrealized loss position, total, fair value	2,827,554	5,078,176
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(109,702)	(155,421)
United States Government Full Faith and Credit [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	508	0
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(4)	0
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	0	498
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	0	(15)
Available for sale securities, continuous unrealized loss position, total, fair value	508	498
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(4)	(15)
United States Government Sponsored Agencies [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	585,574	0
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(8,671)	0
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	0	610,339
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	0	(13,933)
Available for sale securities, continuous unrealized loss position, total, fair value	585,574	610,339
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(8,671)	(13,933)
United States Municipalities, States and Territories [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	50,040	0
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(322)	0
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	2,945	27,947
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(55)	(711)
Available for sale securities, continuous unrealized loss position, total, fair value	52,985	27,947
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(377)	(711)
Foreign Government Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	9,044	14,194
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(1,232)	(1,068)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	11,251	11,542
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(3,168)	(2,885)
Available for sale securities, continuous unrealized loss position, total, fair value	20,295	25,736
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(4,400)	(3,953)
Corporate Securities [Member] \| Finance, Insurance and Real Estate [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	182,005	253,439
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(1,464)	(2,586)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	79,738	399,874
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(10,022)	(16,277)
Available for sale securities, continuous unrealized loss position, total, fair value	261,743	653,313
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(11,486)	(18,863)
Corporate Securities [Member] \| Manufacturing, Construction and Mining [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	703,225	1,078,089
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(30,909)	(35,151)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	235,075	694,088
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(24,455)	(35,926)
Available for sale securities, continuous unrealized loss position, total, fair value	938,300	1,772,177
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(55,364)	(71,077)
Corporate Securities [Member] \| Utilities and Related Sectors [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	339,510	373,952
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(10,650)	(8,185)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	64,467	344,313
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(2,500)	(10,153)
Available for sale securities, continuous unrealized loss position, total, fair value	403,977	718,265
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(13,150)	(18,338)
Corporate Securities [Member] \| Wholesale/Retail Trade [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	71,296	88,766
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(1,058)	(2,290)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	23,733	99,427
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(2,727)	(3,122)
Available for sale securities, continuous unrealized loss position, total, fair value	95,029	188,193
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(3,785)	(5,412)
Corporate Securities [Member] \| Services, Media and Other [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	149,762	131,940
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(1,234)	(1,567)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	37,022	277,296
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(1,126)	(8,139)
Available for sale securities, continuous unrealized loss position, total, fair value	186,784	409,236
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(2,360)	(9,706)
Corporate Securities [Member] \| Insurance [Member]
Held-to-maturity Securities, Continuous Unrealized Loss Position [Abstract]
Held for investment securities, continuous unrealized loss position, less than 12 months, fair value		0
Held for investment securities, continuous unrealized loss position, less than 12 months, unrealized losses		0
Held for investment securities, continuous unrealized loss position, 12 months or longer, fair value		75,838
Held for investment securities, continuous unrealized loss position, 12 months or longer, unrealized losses		(594)
Held for investment securities, continuous unrealized loss position, total, fair value		75,838
Held for investment securities, continuous unrealized loss position, total, unrealized losses		(594)
Residential Mortgage Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	13,147	22,115
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(149)	(1,219)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	7,292	20,427
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(1,365)	(986)
Available for sale securities, continuous unrealized loss position, total, fair value	20,439	42,542
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(1,514)	(2,205)
Commercial Mortgage Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	110,898	241,637
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(454)	(1,344)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	0	187,241
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	0	(1,979)
Available for sale securities, continuous unrealized loss position, total, fair value	110,898	428,878
Available for sale securities, continuous unrealized loss position, total, unrealized losses	(454)	(3,323)
Other Asset Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Available for sale securities, continuous unrealized loss position, less than 12 months, fair value	125,651	142,094
Available for sale securities, continuous unrealized loss position, less than 12 months, unrealized losses	(1,533)	(3,519)
Available for sale securities, continuous unrealized loss position, 12 months or longer, fair value	25,371	58,958
Available for sale securities, continuous unrealized loss position, 12 months or longer, unrealized losses	(6,604)	(4,366)
Available for sale securities, continuous unrealized loss position, total, fair value	151,022	201,052
Available for sale securities, continuous unrealized loss position, total, unrealized losses	$ (8,137)	$ (7,885)

Investments (Gross Unrealized Losses on Investments, By Category and Length of Time) (Details) (Fixed Maturity Securities [Member], USD $)
In Thousands, unless otherwise specified