Accumulated Other Comprehensive Income (Loss) - Details About AOCI Components (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments sold	$ 43,357	$ 15,800	$ 84,504	$ 57,567
OTTI on investments	(1,561)	(16,168)	(5,289)	(34,733)
Total before tax	(40,858)		(77,258)
Provision (benefit) for income tax	(28,872)	(29,812)	(72,351)	(51,362)
Unrealized gains (losses) on investments
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments sold	(56,969)		(102,391)
OTTI on investments	1,561		5,288
Total before tax	(55,408)		(97,103)
Provision (benefit) for income tax	(3,560)		(3,286)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(58,968)		(100,389)
OTTI losses recognized in AOCI
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	14,440		19,625
Cash flow hedge
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	110		220
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(40,858)		(77,258)
Provision (benefit) for income tax	(3,562)		(3,291)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(44,420)		(80,549)
Reclassification out of Accumulated Other Comprehensive Income [Member] | OTTI losses recognized in AOCI
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments sold	13,612		17,887
OTTI on investments	828		1,738
Total before tax	14,440		19,625
Provision (benefit) for income tax	(2)		(5)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	14,438		19,620
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash flow hedge
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	110		220
Provision (benefit) for income tax	0		0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 110		$ 220