Fair Value Measurements (Details 4) (USD $) In Thousands, unless otherwise specified			6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Minimum	Jun. 30, 2013 Maximum	Jun. 30, 2013 Carrying amount	Dec. 31, 2012 Carrying amount	Jun. 30, 2013 Estimated fair value	Dec. 31, 2012 Estimated fair value
Assets
Mortgage loans on real estate	$ 3,057,906	$ 2,881,758			$ 3,057,906	$ 2,881,758	$ 3,145,236	$ 3,114,796
Policy loans	4,181,279	4,260,200			4,181,279	4,260,200	4,181,279	4,260,200
Limited partnership interests					47,438	46,707	46,896	43,954
Other investments	19,682	21,328			18,497	18,890	44,696	45,050
Liabilities
Annuity contract benefits without life contingencies					9,757,842	9,622,357	9,508,711	9,731,734
Policyholders' funds	373,373	374,821			373,373	374,821	373,373	374,821
Commercial paper	93,788	97,987			93,788	97,987	93,788	97,987
Notes payable due to parent					$ 532,505	$ 532,491	$ 545,922	$ 563,860
Estimated liquidation period of underlying assets of the funds			1 year	10 years
Interest Crediting Rate Change Minimum Notice			30 days