Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	$ 6,030,976	[1]	$ 5,784,205	[1]
Amortized Cost/Cost, Equity securities	85,428		84,754
Unrealized Gains	434,240	[1]	344,286	[1]
Unrealized Losses	66,774	[1]	118,918	[1]
Fair Value	6,398,442	[1]	6,009,573	[1]
Fair Value, Equity securities	94,189		91,858
OTTI in AOCI	2,866	[1],[2]	2,812	[1],[2]
Mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	550,737	[1]	555,574	[1]
Unrealized Gains	39,324	[1]	33,711	[1]
Unrealized Losses	12,793	[1]	19,560	[1]
Fair Value	577,268	[1]	569,725	[1]
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	467,644	[1]	449,060	[1]
Unrealized Gains	13,849	[1]	9,865	[1]
Unrealized Losses	14,503	[1]	23,351	[1]
Fair Value	466,990	[1]	435,574	[1]
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	1,444,604	[1]	1,425,441	[1]
Unrealized Gains	117,437	[1]	80,701	[1]
Unrealized Losses	15,882	[1]	34,615	[1]
Fair Value	1,546,159	[1]	1,471,527	[1]
OTTI in AOCI	0	[1],[2]	0	[1],[2]
Foreign government bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	50,623	[1]	50,641	[1]
Unrealized Gains	5,397	[1]	4,700	[1]
Unrealized Losses	157	[1]	390	[1]
Fair Value	55,863	[1]	54,951	[1]
OTTI in AOCI	0	[1],[2]	0	[1],[2]
Corporate bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	2,572,505	[1]	2,457,727	[1]
Unrealized Gains	229,135	[1]	188,832	[1]
Unrealized Losses	17,002	[1]	32,150	[1]
Fair Value	2,784,638	[1]	2,614,409	[1]
OTTI in AOCI	0	[1],[2]	0	[1],[2]
Other mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	944,863	[1]	845,762	[1]
Unrealized Gains	29,098	[1]	26,477	[1]
Unrealized Losses	6,437	[1]	8,852	[1]
Fair Value	967,524	[1]	863,387	[1]
OTTI in AOCI	2,866	[1],[2]	2,812	[1],[2]
Equity securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost, Equity securities	85,428		84,754
Unrealized Gains	11,261		10,723
Unrealized Losses	2,500		3,619
Fair Value, Equity securities	94,189		91,858
OTTI in AOCI	$ 0	[1],[2]	$ 0	[1],[2]

[1] Fair value includes securities issued by Federal National Mortgage Association (“FNMA”) of $343,090 and $336,193; Federal Home Loan Mortgage Corporation (“FHLMC”) of $434,214 and $427,172; and Government National Mortgage Association (“GNMA”) of $132,896 and $126,245 as of March 31, 2014 and December 31, 2013, respectively.

[2] 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.