Fair Value Measurements (Details 4) (USD $) In Thousands, unless otherwise specified			9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Minimum	Sep. 30, 2013 Maximum	Sep. 30, 2013 Carrying amount	Dec. 31, 2012 Carrying amount	Sep. 30, 2013 Estimated fair value	Dec. 31, 2012 Estimated fair value
Assets
Mortgage loans on real estate	$ 3,039,245	$ 2,881,758			$ 3,039,245	$ 2,881,758	$ 3,132,774	$ 3,114,796
Policy loans	4,145,260	4,260,200			4,145,260	4,260,200	4,145,260	4,260,200
Limited partnership interests					46,885	46,707	46,239	43,954
Other investments	17,476	21,328			16,360	18,890	42,895	45,050
Liabilities
Annuity contract benefits without life contingencies					10,106,819	9,622,357	9,784,830	9,731,734
Policyholders' funds	326,639	374,821			326,639	374,821	326,639	374,821
Commercial paper	99,988	97,987			99,988	97,987	99,988	97,987
Notes payable due to parent					$ 541,770	$ 532,491	$ 548,902	$ 563,860
Estimated liquidation period of underlying assets of the funds			1 year	10 years
Interest Crediting Rate Change Minimum Notice			30 days