Investments (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	$ 6,323,042		$ 5,784,205
Amortized Cost/Cost, Equity securities	97,757		84,754
Unrealized Gains	503,520		344,286
Unrealized Losses	33,093		118,918
Fair Value	6,793,469		6,009,573
Fair Value, Equity securities	106,837		91,858
OTTI in AOCI	2,880	[1]	2,812	[1]
Mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	494,650	[2]	555,574	[2]
Unrealized Gains	44,197	[2]	33,711	[2]
Unrealized Losses	4,334	[2]	19,560	[2]
Fair Value	534,513	[2]	569,725	[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	490,611	[2]	449,060	[2]
Unrealized Gains	20,583	[2]	9,865	[2]
Unrealized Losses	7,482	[2]	23,351	[2]
Fair Value	503,712	[2]	435,574	[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	1,460,938		1,425,441
Unrealized Gains	162,032		80,701
Unrealized Losses	5,865		34,615
Fair Value	1,617,105		1,471,527
OTTI in AOCI	0	[1]	0	[1]
Foreign government bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	52,571		50,641
Unrealized Gains	6,268		4,700
Unrealized Losses	60		390
Fair Value	58,779		54,951
OTTI in AOCI	0	[1]	0	[1]
Corporate bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	2,624,428		2,457,727
Unrealized Gains	240,948		188,832
Unrealized Losses	9,608		32,150
Fair Value	2,855,768		2,614,409
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	1,199,844		845,762
Unrealized Gains	29,492		26,477
Unrealized Losses	5,744		8,852
Fair Value	1,223,592		863,387
OTTI in AOCI	2,880	[1]	2,812	[1]
Equity securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost, Equity securities	97,757		84,754
Unrealized Gains	11,882		10,723
Unrealized Losses	2,802		3,619
Fair Value, Equity securities	106,837		91,858
OTTI in AOCI	$ 0	[1]	$ 0	[1]

[1] Related to securities for which an unrealized loss was bifurcated to distinguish the credit related portion and the portion driven by other market factors. Represents the amount of other-than-temporary impairment losses in AOCI which was not included in earnings; amounts also include unrealized gains/(losses) on such impaired securities relating to changes in the fair value of those securities subsequent to the impairment measurement date.

[2] Fair value includes securities issued by Federal National Mortgage Association (“FNMA”) of $319,596 and $336,193; Federal Home Loan Mortgage Corporation (“FHLMC”) of $419,913 and $427,172; and Government National Mortgage Association (“GNMA”) of $136,379 and $126,245 as of September 30, 2014 and December 31, 2013, respectively.