Investments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	$ 5,591,125		$ 5,311,457
Equity securities, Amortized Cost/Cost	78,016		52,396
Unrealized Gains	414,120		660,665
Unrealized Losses	74,631		9,890
Fair value of issued securities	5,930,614		5,962,232
Equity securities, Fair Value	83,040		53,503
OTTI in AOCI	2,653	[1]	3,214	[1]
Mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	573,425	[2]	547,040	[2]
Unrealized Gains	46,609	[2]	72,644	[2]
Unrealized Losses	6,165	[2]	125	[2]
Fair value of issued securities	613,869	[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	431,906	[2]	371,706	[2]
Unrealized Gains	17,819	[2]	37,857	[2]
Unrealized Losses	11,420	[2]	135	[2]
Fair value of issued securities	438,305	[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	1,413,405		1,402,424
Unrealized Gains	115,166		186,261
Unrealized Losses	20,322		2,648
Fair value of issued securities	1,508,249		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	49,517		48,476
Unrealized Gains	5,913		9,393
Unrealized Losses	216		0
Fair value of issued securities	55,214		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	2,344,406		2,258,554
Unrealized Gains	197,675		313,430
Unrealized Losses	28,376		4,950
Fair value of issued securities	2,513,705		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	778,466		683,257
Unrealized Gains	30,938		41,080
Unrealized Losses	8,132		2,032
Fair value of issued securities	801,272		722,305
OTTI in AOCI	2,653	[1]	3,214	[1]
Equity securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Equity securities, Amortized Cost/Cost	78,016		52,396
Unrealized Gains	6,373		2,397
Unrealized Losses	1,349		1,290
Equity securities, Fair Value	83,040		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 $383,040 and $375,111; Federal Home Loan Mortgage Corporation (“FHLMC”) of $431,649 and $418,174; and Government National Mortgage Association (“GNMA”) of $130,780 and $136,998 as of June 30, 2013 and December 31, 2012, respectively.