Restatement of Previously Issued Condensed Consolidated Financial Statements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Fixed maturities, available-for-sale, at fair value	$ 16,281,559		$ 18,188,344
Total investments	25,839,032		26,110,376
Deferred acquisition costs and value of business acquired	314,368		204,461
Investment income due and accrued	241,110		257,028
Due from parent and affiliates	91,003		82,828
Other assets	659,179		609,623
Total assets	53,355,181		52,818,605
Future policy benefits	23,792,497		23,480,618
Total policy benefit liabilities	24,562,332		24,250,309
Deferred income tax liabilities, net	121,157		288,995
Other liabilities	746,545		719,969
Total liabilities	51,525,237		50,682,308
Accumulated other comprehensive income (loss)	311,682	618,504	635,699	562,741	485,845	469,982
Retained earnings	738,870		722,525	681,560
Total stockholder's equity	1,829,944		2,136,297	2,020,747		1,914,073
Total liabilities and stockholder's equity	53,355,181		52,818,605
Fixed maturities, available-for-sale, amortized cost	15,509,767		16,756,216
As previously reported
Fixed maturities, available-for-sale, at fair value	18,209,545
Total investments	27,767,018
Deferred acquisition costs and value of business acquired	272,466
Investment income due and accrued	241,889
Due from parent and affiliates	71,491
Other assets	654,493
Total assets	55,217,846
Future policy benefits	23,749,694
Total policy benefit liabilities	24,519,529
Repurchase agreements	1,894,338
Deferred income tax liabilities, net	124,047
Other liabilities	710,799
Total liabilities	53,343,916
Accumulated other comprehensive income (loss)	300,808			564,251
Retained earnings	793,730			677,654
Total stockholder's equity	1,873,930			2,018,351
Total liabilities and stockholder's equity	55,217,846
Fixed maturities, available-for-sale, amortized cost	17,457,961
Adjustments for accounting for forward settling to be announced (TBA) security transactions, plan sponsor expense accounts, and deferred acquisition costs (DAC) | Adjustments
Fixed maturities, available-for-sale, at fair value	(1,927,986)
Total investments	(1,927,986)
Deferred acquisition costs and value of business acquired	41,902
Investment income due and accrued	(779)
Due from parent and affiliates	19,512
Other assets	4,686
Total assets	(1,862,665)
Future policy benefits	42,803
Total policy benefit liabilities	42,803
Repurchase agreements	(1,894,338)
Deferred income tax liabilities, net	(2,890)
Other liabilities	35,746
Total liabilities	(1,818,679)
Accumulated other comprehensive income (loss)	10,874			(1,510)
Retained earnings	(54,860)			3,906
Total stockholder's equity	(43,986)			2,396
Total liabilities and stockholder's equity	(1,862,665)
Fixed maturities, available-for-sale, amortized cost	$ (1,948,194)