Investments (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	$ 5,662,718		$ 5,311,457
Equity securities, Amortized Cost/Cost	83,079		52,396
Unrealized Gains	374,666		660,665
Unrealized Losses	96,862		9,890
Fair Value	5,940,522		5,962,232
Equity securities, Fair Value	86,631		53,503
OTTI in AOCI	2,786	[1]	3,214	[1]
Mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	559,749	[2]	547,040	[2]
Unrealized Gains	40,317	[2]	72,644	[2]
Unrealized Losses	12,705	[2]	125	[2]
Fair Value	587,361	[2]	619,559	[2]
OTTI in AOCI	0	[1],[2]	0	[1],[2]
Other, including U.S. Treasury Securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	455,923	[2]	371,706	[2]
Unrealized Gains	13,523	[2]	37,857	[2]
Unrealized Losses	14,345	[2]	135	[2]
Fair Value	455,101	[2]	409,428	[2]
OTTI in AOCI	0	[1],[2]	0	[1],[2]
Municipal bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	1,395,769		1,402,424
Unrealized Gains	93,091		186,261
Unrealized Losses	29,249		2,648
Fair Value	1,459,611		1,586,037
OTTI in AOCI	0	[1]	0	[1]
Foreign government bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	49,501		48,476
Unrealized Gains	5,169		9,393
Unrealized Losses	349		0
Fair Value	54,321		57,869
OTTI in AOCI	0	[1]	0	[1]
Corporate bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	2,391,920		2,258,554
Unrealized Gains	193,315		313,430
Unrealized Losses	31,811		4,950
Fair Value	2,553,424		2,567,034
OTTI in AOCI	0	[1]	0	[1]
Other mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	809,856		683,257
Unrealized Gains	29,251		41,080
Unrealized Losses	8,403		2,032
Fair Value	830,704		722,305
OTTI in AOCI	2,786	[1]	3,214	[1]
Equity securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Equity securities, Amortized Cost/Cost	83,079		52,396
Unrealized Gains	7,225		2,397
Unrealized Losses	3,673		1,290
Equity securities, Fair Value	86,631		53,503
OTTI in AOCI	$ 0	[1]	$ 0	[1]

[1] Represents the amount of other-than-temporary impairment losses in AOCI which, beginning April 1, 2009, was not included in earnings under current accounting guidance. Amounts also include unrealized gains/losses on impaired securities relating to changes in the fair value of such securities subsequent to the impairment measurement date.

[2] Fair value includes securities issued by Federal National Mortgage Association (“FNMA”) of $364,823 and $375,111; Federal Home Loan Mortgage Corporation (“FHLMC”) of $439,184 and $418,174; and Government National Mortgage Association (“GNMA”) of $126,881 and $136,998 as of September 30, 2013 and December 31, 2012, respectively.