Fair Value Measurements (Details 5) (USD $) In Thousands, unless otherwise specified			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Minimum	Dec. 31, 2012 Maximum	Dec. 31, 2012 Carrying amount	Dec. 31, 2011 Carrying amount	Dec. 31, 2012 Estimated fair value	Dec. 31, 2011 Estimated fair value
Assets
Mortgage loans on real estate	$ 2,881,758	$ 2,513,087			$ 2,881,758	$ 2,513,087	$ 3,114,796	$ 2,679,474
Policy loans	4,260,200	4,219,849			4,260,200	4,219,849	4,260,200	4,219,849
Limited partnership interests					46,707	48,053	43,954	41,931
Other investments	21,328	22,990			18,890	22,990	45,050	47,915
Liabilities
Annuity contract benefits without life contingencies					9,622,357	8,727,286	9,731,734	8,888,585
Policyholders' funds	374,821	382,816			374,821	382,816	374,821	382,816
Commercial paper	97,987	97,536			97,987	97,536	97,987	97,536
Notes payable					$ 532,491	$ 532,463	$ 563,860	$ 515,104
Estimated liquidation period of underlying assets of the funds			1 year	10 years
Interest Crediting Rate Change Minimum Notice			30 days