Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	$ 317,657	$ 353,472	$ 647,943
Realized and unrealized gains (losses) included in net income	(3,758)	3,806	(48,952)
Realized and unrealized gains (losses) included in other comprehensive income (loss)	37,063	21,078	76,439
Sales	(3,595)	(16,277)
Settlements	(42,717)	(48,924)
Purchases, issuances and settlements			(132,433)
Transfers into Level 3		8,733
Transfers out of Level 3	(37,258)	(4,231)
Transfers in (out) of Level 3			(189,525)
Balance at the end of the period	267,392	317,657	353,472
Fixed maturities available-for-sale, Corporate debt securities
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	36,496	58,692	188,936
Realized and unrealized gains (losses) included in net income	(66)	3,961	475
Realized and unrealized gains (losses) included in other comprehensive income (loss)	102	779	5,630
Sales	(1,598)	(14,430)
Settlements	(874)	(17,460)
Purchases, issuances and settlements			(30,084)
Transfers into Level 3		7,333
Transfers out of Level 3	(32,238)	(2,379)
Transfers in (out) of Level 3			(106,265)
Balance at the end of the period	1,822	36,496	58,692
Fixed maturities available-for-sale, Asset-backed securities
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	279,021	290,488	392,365
Realized and unrealized gains (losses) included in net income		(192)	(49,393)
Realized and unrealized gains (losses) included in other comprehensive income (loss)	33,346	20,031	70,026
Settlements	(41,809)	(31,306)
Purchases, issuances and settlements			(98,807)
Transfers out of Level 3	(5,020)
Transfers in (out) of Level 3			(23,703)
Balance at the end of the period	265,538	279,021	290,488
Fixed maturities available-for-sale, Commercial mortgage-backed securities
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period			58,270
Transfers in (out) of Level 3			(58,270)
Fixed maturities available-for-sale, Collateralized debt obligations
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	22	14	1,729
Realized and unrealized gains (losses) included in net income			(34)
Realized and unrealized gains (losses) included in other comprehensive income (loss)	11	8	161
Settlements	(1)
Purchases, issuances and settlements			(1,842)
Balance at the end of the period	32	22	14
Derivative instruments
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period			(3,317)
Transfers in (out) of Level 3			3,317
Separate accounts
Recurring Level 3 financial assets and liabilities
Balance at the beginning of the period	2,118	4,278	9,960
Realized and unrealized gains (losses) included in net income	(3,692)	37
Realized and unrealized gains (losses) included in other comprehensive income (loss)	3,604	260	622
Sales	(1,997)	(1,847)
Settlements	(33)	(158)
Purchases, issuances and settlements			(1,700)
Transfers into Level 3		1,400
Transfers out of Level 3		(1,852)
Transfers in (out) of Level 3			(4,604)
Balance at the end of the period		$ 2,118	$ 4,278